a couple questions about nintendo 3ds r4 cards?

a couple questions about nintendo 3ds r4 cards?

1. if i use the r4 software can i have stuff downloaded from the e-store on the same card. like i know in my psp my pro duo has my homebrew stuff but also any stuff downloaded from PSN is it the same
2. how would i go about playing my GBA and my nintendo DS backups with the card is it like a psp homebrew where u need to get another program or can i just select them. if i need a different program can u give me a link
3. is there a card that would be better for playing backups or are they all basically the same thing
4. where is the best sites to buy the r4 cards from
ignore question 1 i just remembered that the card does not go in the sd card slot