If you want a good Slot-1 card, you should either get the M3 Simply or the CycloDS Evolution (supports up to 16GB)
The M3 Simply is about $35 and the CycloDS Evolution is I think $75, you should be able to get the Slot-1 cards at either Divineo or Gameyeeeah.
Just about any Slot-1 card can play homebrew games and videos. As for the backup part, I can't answer that because it's against the rules.
I don't know about which MicroSD card to use, I think that any MicroSD should work.
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