1. You'll have to replace the thing you messed up with the original file.
All of the files in the game can be found here (For NTSC/NTSJ):
https://www.dropbox.com/s/p01chjw1j1k4zuzor here (For PAL):
www.mediafire.com/?obemxmzbcvb6dThe repositories mimic the insides of the Brawl Disc, so it should be easy to find things inside it.
Keeping backups when you're doing stuff like this will prevent you from ever having to go online to get original files, though.
2. Not that I know of. Sorry.
3. It's VERY simple. Just replace all of the files given to you, just like the costumes.
FitChar.Pac - Contains Moveset data. (This is necessary for new movesets.)
FitCharXX.pac
FitCharXX.pcs
- Contain costumes for you character. May or May not be necessary for your new moveset.
More often than not, though, you'll need them.
FitCharMotionEtc.pac - Contains Animation and Extra Model data.
- Generally, only REALLY old PSAs don't have one of these. If you get one, USE IT, because it's necessary.
Those are the general files. If you get other things, like: (FitCharDark.Pac, or FitCharEntry.pac, or FitCharFinal.pac)
...You'll need to use those, too.
It's really time-consuming to put full movesets inside the game using WiiScrubber, but nothing can be done about that.
4.
Well, there are various game controllers you can buy that are directly designed for your computer. If you're savvy, you can buy converters for your PS2 Controllers. PS3 Controllers have MotionJoy, a program that allows use of them on computers. There are GameCube-to-USB converters floating around as well. Wireless Xbox controllers have a wireless adapter that allows them to be used with machines other than 360s. Wired Xbox Controllers are automatically usable with PCs. (Not sure about Macs. Linux should probably be fine.) You can buy Generic Bluetooth Hubs that are compliant with Windows 7 which will allow you to hook up Wii controllers (and any applicable accessories) directly up to the computer. Along with that, you can actually connect a sensorbar to your computer too.
I myself have a PS2-USB converter, PS3 MotionJoy, and Wired Xbox for my Dolphin.
If you really like your graphics, there's an HD HUD pack for Dolphin-Only users here:
http://forums.kc-mm.com/Gallery/BrawlView.php?Number=30523 I don't use it though, so you'll have to check that out yourself.