SD card size doesn't matter, and most brands should work. A couple are incompatible, but that's unavoidable sadly.
Anyway, check your version number in Settings. If you do have 4.2, you need to use bannerbomb v2. If you have 4.1 or lower, I'd advise you to update to the latest version first, then use bannerbomb v2. If you can't/don't want to update, use bannerbomb v1.
Use bannerbomb to run the HackMii Installer v0.6. In it, choose what you want to install. You need to install HBC, and I'd advise DVDx as well in case you ever want to watch DVDs. You won't be able to install BootMii as boot2, but you can install it as an IOS if you like. But know that it is not very useful as IOS at the moment.
Next, download the emulators you want. You need to setup your SD card as follows; in the root (i.e. not inside any folders, e.g. if your SD card has the letter F on windows, the root would be F:/) make a folder called "apps" (all lower case). Inside this, make a folder for each emulator/piece of homebrew you wish to run. (e.g. F:/apps/SNES9X). Inside this, place the boot.dol, icon.png and meta.xml from the download of the homebrew. Some homebrew also has extra files, which usually also have to go into this directory. Check each homebrew's readme if you're not sure.
Finally, when you launch HBC with your SD card inserted, each homebrew should show up. Just point and press A, then select "Load" to launch it.
For more information, and in depth instructions of what I said above, check [
www.wiibrew.org]