More questions :-)
1. Mysticales mentioned that maybe backups of NDS ROMs maybe not work on WFC? Is that correct? I'm quite sure it can.
2. Need to confirm also that you can put several NDS images onto one SD Card? M3 will let you choose which game to play etc?
3. Can you mix and match ROMs? Eg, put a few NDS and GBA on one SD Card?
4. What about a bit of everything? Eg NDS, GBA, MP3 etc. I guess you just need the right app and it should all run fine?