1) The adventuring polymath. I loved the factotum-- especially a certain changeling factotum. Mechanically, I loved the inspiration points and the chance to try out a different wacky Skill application every encounter because I just could. Being able to trot out a spell in a pinch was fun (though I confess, it was most often polymorph), and it was comforting to know that just about any weapon I chose to include in a disguise was more than a prop. Conceptually, I guess this would be a less- fisticuffs-more-book-quoting Indiana Jones, or alternately, a more-fisticuffs-less-cocaine Sherlock Holmes (who was quiet the disguise artist, some people overlook).
That one is tricky. The factotum is a class designed within the 3e system, a class built for the rules mastery subset. That's why the CO guys loved it so much.
That said, I see a few ways to go about it. Doppleganger as a race is a start, and with the +2 int and cha, it will work well with class choices and the skills you want to emphasize (change shape, a decent Cha, and a high bluff skill and you will be a master of disguise). Jack of all trades is a necessary feat, making you half trained in everything you aren't trained in. Class is giving me a bit of trouble. It'd help to know exactly what you want out of combat with this one. If you literally mean "a spell in a pinch" then wizard multiclass onto something else would be really good, as it gives you exactly that, a wizard at-will as an encounter power with the the option to pick up a couple more spells via feats. OTOT, wizard has the best set of utility powers for a character like what you describe, and you can only get one of those with multiclassing. Plus, rituals would be useful. So maybe wizard main class and multiclass something else appropriate, any multiclass feat gives you some power from another class, which is a part of the factotums "thing".
You know, for a minor rules tweak you could go pretty far with this. It's a rule that you can only take one multiclass feat, but with a DM that gives you an exception to that, you could just take them all (or near enough), gaining a whole suite of other classes basic powers and a bunch of trained skills. If that's the case, your main class could be something more martial, to give you that weapons knowledge, then you'd end up with a couple spells, a bit of healing, some one shot tricks for extra damage (limited mark, quarry, sneak attack). I'd allow it as it would be an interesting character. But if not, wizard/x or x/wizard would be good. Ritual caster and/or alchemist would enhance the variety of "tricks" at your disposal.
2) The angelic avatar. Another oddball I loved for all its faults was the incarnate. Leaving aside legitimate concerns about soul-sandals and obsessions with the color blue, I really dug how incarnum worked, and the fact that a low-level character had access to some pretty dramatic soulmelds. In particular, I wrote up a lawful good incarnate who, using the Incarnate Avatar and Incarnate Weapon melds, did a pretty good job of impersonating a Shavarath angel or solar (see: Eberron cosmology) at an early level. Conceptually, this is a hardcore soldier-for-good who looks like a peaceful and un-armored fluffy, and is all the scarier for it when swooping down into the fray and brandishing the righteous sword of the Silver Flame. (Note: Incarnate Avatar didn't really grant flight until later levels, so getting any sort of non-cosmetic effect out of the wings before, say, 15th level would be groovy with me.)
I'm not very familiar with the incarnate at all, so I don't know how much help I can be on this one. Hardcore soldier for good would be a LG Paladin. Is there glamored armor yet in 4e (don't have AV nearby)? No currently available race fits very well, you'd have to reflavor something - maybe Eladrin as the base, but angelic and with wings, you could flavor your feystep into limited flight, even from 1st level. That's about all I got on this one not being familiar with it at all, but it seems a hard conversion.
3) The firebreathing squad captain. Coming on the heals of the 3.5 warlock, I was also impressed by the dragonfire adept. Great utility invocations and an area attack breath weapon-- what's not to love? I tended to come back to a human House Deneith dragonfire adept (again, see Eberron) who approached the class as a warmage tradition-- leading by example on the front line and breathing fire all over the damned place. ("Stand behind me-- this is going to get hot. Or cold, depending on their resistances.") A somewhat limited toolset, come to think of it, but very good at rephrasing every screw problem in nail terms. Target exclusion and element resistance a plus!
This one is a bit easier. Dragonborn warlord/wizard (take thunderwave as your encounter power, a front line bad ass nail if there ever was one). Couple feats for a couple more useful, front line wizard powers like Burning Hands or Fire Shroud (color to match with your breath choice). Flavor your warlord powers to be a bit more arcane, perhaps. Or for a more caster flavor, go wizard/warlord, you gain inspiring word which is very leader-ly, focus on close burst powers, pick up a solid weapon and some armor feats.
While I don't have FR, swordmage could be more ideal for this, and likely is. Dragonborn swordmage probably fits the bill well. Multi into warlord for inspiring word and some leader powers if needed.
