Visit the Brawl+ site, they have a premade package to put on the SD card that installs Brawl+ and the Homebrew Browser so you can find more homebrew apps.
Downgrading bricks your Wii half the time, and even if you have 4.2 (the latest update), you can still install homebrew! DX The new method Bannerbomb works on anything 3.4 and higher (or was it 3.5 and higher... whatever). Anything lower, the Twilight Hack works. No downgrading, GC. =P
You obviously want a "yes" under homebrew. :P I personally use a PNY Optima 2GB SD card. If you can find said SD card, I can guarentee it'l give you no problems. Anything on the list with a "yes" should be fine too, though.