1. I'm going to comment on smallest height/weight brawler because that is what I mainly use. Small brawler is also probably the best brawler.
The main combo you're wanting to use is Dthrow -> Fair -> Helicopter Kick (2nd up special). This will generally work once you learn how to read the opponent's DI, and around the ledge this can kill as early as 20% (assuming you have rage). However, this stops working around 50-60 percent.
Outside of this, you have Uair -> Helicopter Kick, which works around 60-90%. If you're closer to the side, it will kill consistently. If you're high up, it will generally kill off of the top. Bair -> Helicopter Kick will also work if they're DI'ing towards you and you're not retreating the Bair. Dtilt can combo into Fair -> Helicopter Kick or just Helicopter Kick at lower percents as well.
I don't know if this falls under tricks, but Nair out of shield and Helicopter Kick out of shield are both very important tools to master with this character. Nair is your general hitbox you can throw out of shield that is safe because of your mobility, and Helicopter Kick. Also, cancelling Feint Jump's kick (2nd down special) with the ledge is a very useful tool to have, especially since the kick can combo into Helicopter Kick (and if you catch them with it in that position, it will probably kill at 30-40%).
Also just so you know, you're going to get most of your kills from Helicopter Kick, but U-Smash also kills. Dair auto cancels and kills as well, so throwing it out isn't a bad idea as long as you're not super predictable with it. Side-special 1 (I don't remember the name) kills, but it's kind of inconsistent and should probably only be used to hard punish a spot dodge. D-Smash can catch people recovering to the ledge (back hit will kill earlier). F-Smash has a lot of ending lag, so only use it as a hard punish.
2. As others have said, this is a debate that is going on at the moment. However, this will turn into something that differs between regions. You should ask your local TO's about what they're doing with Mii Fighters. You have a way better shot of convincing your local TO's that they should allow Mii Fighters to use all of their sets than you do convincing the masses. Trust me.
If you're wanting to use a Mii but you're forced into 1111, Gunner/Sword Fighter aren't bad choices. Brawler is the worst choice out of the three. 1111 default-sized brawler is probably bottom 5 (maaaybe bottom 10) and he has no hope of getting better through patches, so don't even bother in that regards.
If you're using small brawler, you generally want to choose 1122 or 2122. Honestly, the neutral special 1/2 depends on the matchup. Small brawler has enough mobility to where he can use Shot Put (1st neutral special) safely against characters that aren't high mobility like Sonic, Pikachu, Sheik, and Greninja, and it helps in quite a few matchups where the opponent is super zoney and won't let you in (Custom Villager is a good example). The uppercut (2nd neutral special) is a great kill option regardless, though. You can use 1132 or 2132, but I can't give any advice with that. I've never used Piston Punch (3rd up special).
3. The only thing Puffster didn't go in depth about that I can add here is the ability to mix up his recovery. Feint Jump is an amazing tool to mix your recovery up, and the fact that you have so much aerial mobility after using Helicopter Kick means that you're harder to punish than most characters are after they use up-b (meaning most people can only get a dash attack/grab off on you when they're punishing you). This goes under mobility, but I figured that I would explain a bit more.
You've chosen a rough time to start considering Brawler. I highly recommend talking to your local TO's to figure out what they're doing with Mii Fighters before committing any time to Brawler.