I've been thinking about the bad points of 5e...
There are three big flaws with the system, and I think there's a simple way to fix all three.
1. Player characters are all the same. You have the same attributes by point buy, you have the same proficiencies, you have the same equipment, you have the same class features.... so where's the character flavour?
I haven't noticed that. We don't use point buy, though. But the gear is different, and no one has the same class features. But I'm assuming you mean that two fighters will be similar? To me, that's a feature, not a bug, but your tastes may vary.
2. There are no skills anymore. You have proficiency or you don't. That's it, so no fine tuning your character to give them that extra flair; hell there's not even any feats (not really, the few feats that do exist are bare bones at best and you have to give up the attribute increase).
Again, this is a difference in taste. I LOVE the new skills and feats system. It's simple, it lets players try things even if they're unskilled, and the feats always mean something (as opposed to the weapon finesse/toughness/skill focus issue of 3e). I'm all for simpler gameplay.
3. With no magic item economy, the players are easily finding themselves with literally thousands of gold and having little of tangible GAMEPLAY reward to spend it on. Sure they could buy a keep in the mountains but that's flavour, not tangible gameplay bonus. Even if they do buy magic items, there's FAR less magic items.... which would be fine if every damn character didn't get magic, and loads of it. Rangers and Bards get far more magic now, and Rogues and Fighters both have an arcane spellcaster archetype; so making magic items rare and difficult to source makes no sense now.
I dunno about that, but I can see where you're coming from. In my games, so far, the PCs are more broke than they've been in other editions.... due to downtime expenditures. And they're looking at starting up a keep, getting hirelings, etc. But then, I also have limited magic item sales as a possibility (no one's taken me up on it yet, but we're low level).
Characters need DOUBLE the XP stated in the book in order to level up, and all player characters start at 2nd level. The idea behind this is simple; player characters need to stay at lower levels for longer.
This reminds me of Earthdawn. You can level up quickly, but if you do, you don't get all of your classes cool stuff. It's fun, I guess. And I'm all for anything that keeps the PCs lower level.
Characters who gain proficiency in weapons no longer gain them in the same way. If your class grants you 'Martial Weapon Proficiency' or 'Simple Weapon Proficiency', you get to choose ONE weapon in that category that you are proficient with. This means fighters will have to carefully decide what weapons they have trained with... and it makes racial proficiencies more important and thematic.
The racial weapons bit is cool, sure, but I'm not sure about weapon proficiencies. I really don't like em, because they force players into using only one schtick. And I'm all for fighters grabbing a weapon in a pinch and going with it (and not penalizing them for doing it). It also means that if I have a player that uses a trident, I have to suddenly make sure there are magical tridents available, despite "realism" of doing it... or let him never get a magic item. Either way, it sucks. And I've seen in play that when that's the case, all players take the same proficiencies - long sword, long bow, dagger, and club (or some variation thereof). Which is boring.
BUT, if you do it this way, might I suggest cultural weapon proficiencies for human characters?
During gameplay you can spend 250gp to learn a new tool proficiency or language, this takes approximately 6 months of in game time to achieve. This is already in the main rules in the PHB, I intend to expand on this.
I like this rule as well. I kind of want to expand it to include armour, weapons, and maybe even skills.
If you wish, you can use this same method to train in the use of a weapon, armour, skill, save, or spell. You gain proficiency in that weapon, armour, skill, save; or learn that spell. If you don't have spell slots, you cannot learn the spell as you would be unable to cast it... so in effect you're limited to cantrips for none spellcasting classes (nb. Eldritch Blast cannot be taught, attempts to do so always result in the students confusion... those that finally understand and learn the spell find they have inadvertently made a pact and must level up next level as a Warlock, such is the dangers of trying to harness raw magic). Learning spells does mean sourcing either a wizard willing to teach you, or a scroll containing the spell. This means spells above third level will likely be far more expensive than the 250gp needed for basic training, and spells of 7th level and higher will cost as much to gain tutorage in as buying a small castle. Wizards are not quick to trade away their most potent magic.
It's a bit finicky for my tastes, but it's not going to break your game.
You can speed up this learning process, halving the time to learn to only 3 months, but you must be in seclusion and doing nothing but studying. Learning over 6 months can be done while travelling and living a normal sedentary lifestyle. All learning requires either a tutor, or access to resources, such as a library.
The downside here is, you get your PCs spending a huge amount of time in school, doing... well.... not much. And what do you do as a GM if one PC goes into seclusion to learn a new spell, while everyone else wants to play?
Also, doesn't this mean longer-lived characters are going to do better in your game?
If you already have proficiency, you can still train. Doing so costs the same amount, 250gp and 6 or 3 months game time depending; at the end of which you gain Expertise (as the Rogue class feature), in your chosen tool, skill, or weapon; granting you double your proficiency bonus when using this tool/skill/weapon.
Strongly disagree. Though experience, Expertise is one of the rogue's best abilities. Giving it away for a relatively small cost (considering you expect players to spend a lot of time in downtime), is just screwing over the rogue.
If you already have Expertice in a tool, skill, weapon etc. you can train further and gain Mastery in your choed field. This last stage of training costs 1000gp and takes a minimum of a year (GM discretion), to master; it may even require an adventure in it's own right. Going to a long forgotten ancient library to gain mastery in History, finding a magical portal and travelling to the Feywilds to study first hand for mastery of arcana, travelling to the most inhospitable part of the natural environment and living off nothing but the land for months for mastery of Nature etc...
The idea is cool, but I doubt it'll see much play. A more fun idea (in my opinion) is just to grant this to PCs that have shown aptitude in play, as a result of awesome adventures. The druid who rescues a treant gets mastery in nature; the cleric who has a divine revelation gets mastery in religion; the fighter who climbed the tallest mountain without faltering gets mastery in athletics; etc.
In the case of skills and tools, gaining mastery in them gives you TRIPLE your proficiency score; while with weapons training you get to add your proficiency score to your damage (as well as the double proficiency to hit from expertise), making mastery of a weapon especially potent. Mastery of combat spells is in theory possible, though there's no real recorded examples of someone having managed such a thing.
If you go this route... it'll come back to bite you in your keister. I'd suggest your "mastery" is some sort of advantage. You could even put a rider in there. "I've got mastery history - elvish lore" So, whenever an elvish lore check comes up, the character gets advantage. Giving someone a +12 to a check is HUGE. It's big in pathfinder, even... so it's monstrously big in Fifth.
As for weapons, it's the same issue. Fighters would dish out buttloads of damage... meaning the way to take em down is to destroy their weapon. Which could be tactically fun, but it's a huge burden at the table for the player. A fighter with three or four attacks, with a strength of 20 and a +1 sword, would be doing in your system something like +10 damage per hit. So, assuming a longsword, three attacks, and they all hit, an average of 42 points of damage a round. Which is huge in fifth.
This change gives players a way to "level up" there characters without actually leveling up and the time frame means players have to actively show in gameplay or state during downtime that they're taking this extra training. This will also allow for lower level characters to specialise more, and for well complimentary teams to take down things of higher than normal CR which will naturally feel awesome.
I don't like characters specializing too much. I've played Pathfinder, Shadowrun, and other similar games. Those games reward specialization... and system mastery... and encourage the casual players to sit to the side. I'd rather have a game where everyone at least has a CHANCE to do something (and not be in "well, you could roll a 20...." territory.
But I get your idea, and if that's where you want your game to go, you can edit from there. Tastes vary and all that jazz.