Too much money: My players made me proud by using my own rules against me to quadruple their money, and now they have way too much for 1st level characters. I want to reduce their gold without giving them too much in return; I've been giving them additional rituals in the hope they'll spend some money casting them, but no luck so far. In other games I've offered them magical items at 100% value, which as worked, but in this particular game I'm trying to make magical items a rarity.
Well, as you said, they did it on their own...using your rules. Sounds to me like you have to just eat it and let them enjoy spending their loot. Given that magic items are a rarity, then I second the suggestion to introduce them to "the finer things in life". The finer things are always more expensive.
You could also present them with "investment" or philanthropic opportunities: becoming partners in owning an inn or a tavern or a casino (many a plot hooks possible when the players discover they've inadvertently become financiers for the local organized crime organization.

), donating/replacing the local temple's leaky roof, setting up their own "adventuring company" (which would include, no doubt the requisite adventuring/weapon-baring license from the local authority), or just purchasing a property to set up their own home base/base of operations, the seemingly respectable NPC merchant (or booky?) with the "sure thing" to triple their money, etc...
I also will reiterate the multiple suggestions to simply reduce the treasure found for a while til things even out a bit.
Alternatives to magical items as loot: I've been handing out potions, gemstones, art items, ritual books, wondrous items and information. Yet my players keep looking at me expectantly, waiting for the magic hat of flying donkeys. Suggestions?
The players were aware/told that this game was going to be magic item scarce, right? If not, that's a problem...and for fairness' sake, I'd say you owe them "a hat of flying donkeys"...and THEN make sure they know/notice how scarce magic items are.
I think the suggestion for faulty or cursed items are also a good one. I do not agree that throwing more "single/limited use" items at them is helpful. If magic items are rare...then make them rare. An apothecary with a stock of multiple kinds of potions or a traveling wand salesman in every village doesn't fly. Ritual books and wondrous items? That's magic, no? Why would there be an abundance of books with magical information in it available? If I were a player, I'd want my hat of flying donkeys too if I kept finding potions and wondrous items everywhere.
Information is a good one and the multiple suggestions for important NPCs
who can be helpful (either immediately or in the future) is also always useful. But I doubt it will make your players feel less "cheated" (for lack of a better word) to have a "favor" from some NPC than to have a cool magical weapon they can hit things with.
I've never played with "low magic" or scarce items...sorry can't be more help there.
Passive perception and taking 10: One of my players keeps trying to use his passive perception to make perception skill checks, but I'm insisting that he roll for them. The rules say a character can 'take 10' but I think it's a stupid rule; I only use passive insight and perception when the character isn't making an active check, as you're supposed to, eg. noticing a trap without a check, realizing that you're being lied to without a check, etc.
4e stuff. Sorry, can't help here either. But it would seem, for the sake of common sense, if the player has Passive Perception, then you make the role for them before there's any active search/check. If they don't notice anything on the passive, then the player gets to roll if they make an active attempt. I agree with your insistence he roll for the active check...As for "taking 10" you said it right there, "I think it's a stupid rule." You're the DM. Houserule it and throw the "take 10" out the window.
Stopping mid-dungeon: Whenever we call it for the night, I tell my characters that they were able to take an extended rest at the next session to reset their HP, Healing Surges, etc. How do you handle this?
WOOOAH there, Nelly! I'm with pretty much everyone else. When you stop the session, you hit the pause button.
That said, if the party reaches a place in the dungeon that has been cleared of dangers and relatively safe and we broke for the night then fine, give them their 8 hours of sleep.
If the dungeon is NOT safe (for example, a group of monsters in the next room 30 feet down the hall would equal "not safe"), then break for camping, but roll for random encounters when you start next session to see if they get through enough of the "extended rest" uninterrupted to regain their resources.
But as an "automatic thing", absolutely NOT!
Most of the time in our games (whether I was DMing or not), we would try to stop at a point that made sense. Either A) where the party can camp and rest uninterrupted and/or (more likely) B) immediately following a battle so the stage was clear and set for next time.
This DOES require you to follow, or at least keep in the back of your mind, "in game time."
Picture it. Bucks County, Pennsylvania. 1988. We had broken our camp (we'd established at the end of the last game). We'd done a bit of exploring. Searched a couple of rooms. And MOST of the session was spent on a HUGE, lengthy and very taxing battle with a large group of monsters (I don't at the moment recall what). We were beaten, battered and bereft of many, if not most, spells.
All agreed this was a good time to stop and call it a night. We'd been playing 6 or 7 hours. Our impromptu "leader" character/player says, "Ok. We'll make camp here."
The DM, thoroughly amused, informed/reminded him that it was about 11am in game time. Sure enough, next play session, there we were beaten, battered and bereft of many, if not most, spells...and we went on from there. It's part of the game. Part of the challenge. No rest for the weary.
Food and amenities in dungeon crawls: The adventurers kit contains all that is needed to survive for a few days, but we've never kept a track of it. Does anyone else?
Sometimes yes, sometimes no. For the most part, I played as others here. Let a few days go by unnoticed. Mark the items off/take out the gold for the renewed equipment. Or just not mention it at all and let it be in the background (but NOT for free! Make sure they're spending money or telling you they're foraging/hunting.)
If there is a length of time (I'd say more than a week) where the party is not in a position to replenish their stores, then yes, you need to start keeping track of time -irritability, irrationality, loss of ability bonuses (physical AND mental) and eventual points, dehydration, malnutrition.
Foraging/hunting is usually an option, but depending on terrain, you might not get enough to really meet the whole party's needs.
ALSO, if the party increases! You find/rescue/free a bunch of NPCs who are now with you...the party goes from 4 prepared adventurers to 10 people being herded around until they can be gotten to safety! What are they eating?
Again, as part of the survival element/challenge of the game I think it is worth reminding the party of from time to time, though not keeping constant/strict/not fun records all of the time.
Of course, if your group is a very "by the rules/by the book" sort of group, then yeah, you have to decide to simply NOT include it at all or keep track all of the time. And really...it's not all that much to keep track of. Just goes in with keeping time. Day goes by=deduct a day of rations (or in civilization, deduct xx gp to buy some food).
Role-playing XP: I'm offering 40xp for good roleplaying in game, but I try not to give the same player roleplaying xp twice in a session. when I do so I tell the player why I gave them it, and how they could get it again. How does this play out for other DMs in the long run?
I used to like doing this. But as noted, it can cause problems/dissention among the players as the better/more interested role-players rack up bonuses the others don't...if it is lack of interest, that is one thing. If it is lack of ability, that's another. Some role-players can be annoying as all get out, but they're having a great time. Some people who might WANT to role-play simply don't know how or can't keep up the facade too long.
I would 1) Make it per adventure or reasonable/rational section of an adventure. Not "per session." The person should consistently be able to "keep it up." One session of "great" role-playing doesn't warrant an XP bonus. 2) I would put it on a scale so everyone gets a chance to get something if they put in the effort. 3) I would, as others have suggested, simply wrap it up in the XP allotment/breakdown for each player when XP is doled out, not share the info with everyone. If any player wants an explanation or some "pointers" in how they can increase their bonus, that's a private discussion for them with you. If they want to share the info with each other, that's their business...and could provide some (hopefully mild) confrontation for you.
So as not to make yourself crazy, I'd make the scale simple:
0-Doesn't role-play at all. "I do this. My character does that." Roll dice. Look up stuff in manual. Distract other players. Roll dice some more. Speak about "out of game stuff." Roll dice. Eat all the pizza.
10-Player isn't necessarily consistent with their character's attitude/actions/general M.O. but clearly tries to assert it from time to time.
20-Player is able to provide memorable moments, possibly speaks "in character" sometimes, but does not generally keep up character all of the time.
30- Player presents themselves "in character" most of the time. Player maintains character's actions/attitude/general M.O. even when not speaking in-character.
40- Player role-plays "in character" the entire session AND/OR Player role-plays some intrinsic/quintessential moment for the betterment of their character, the party and the game session as a whole.
Tactics: At a small scale, how do you handle tactics? I've had some good sessions where I used mixed units to make a tactical battle, in particular one game where I used a mixture of swordsmen, halberdiers, and archers to good effect. But what about other things like retreat and surrender?
What everyone else has said. Tactics depend/rely on the conditions of the environment (terrain, weather, temperature, etc.) and the intelligence of the creatures being encountered and, I would add, the length of time the creatures have been there.
Obviously, going into a tribe of orcs' lair will involve significant amounts of tactics with established defenses and procedures to repel invaders. Encountering a warparty in the hilly woods a day or two from their lair would involve different tactics. Entering the lair of an animal intelligence creature will invovle...well, very little tactics besides: "kill (and/or eat) these things coming into my cave" or "run away from these things that have found me."
Surrender is for creatures who are...smart enough to surrender. What happens from the surrender point forward is a matter of alignment and intelligence of the creatures being surrendered TO.
Retreat. That's for anything with enough intelligence to realize if it doesn't leave it's going to die. I would put this at animal intelligence or better. Pretty much all creatures have a "self-preservation" instinct...'cept lemmings of all things for some reason.
Well, hope there's SOME help for you in there someplace.
Most importantly, however you handle things, have FUN!
Happy gaming.
--Steel Dragons
PS: How many of us are making mental notes to create a "magic hat of flying donkeys"? C'mon, be honest.
