I don’t know if you can change your order, but I advice you to get the TV out cable instead of the card reader, you can pick the reader at any computer store for a very low price whatever country you live in, but the TV out cord is another story, were you will have to pay for shipping it to you + it is a little bit more expensive than the card reader, if you were able to change your order know that you will need an extension cable and maybe another converter, but I wouldn't get these now if I were you, I would just leave them for later.
Regarding cards, the main three things you will need a bigger card for are:
1. Movies: Those can be easily re-encoded to maintain quality on GP2X screen but with around 50% decrease in size.
2. NeoGeo big ROMs: Most of the small ROMs collection contains great games so worry not.
3. Collections: like if you wanted to have all known MegaDrive's ROMs, NES ROMs, SNES ROMs, MAME ROMs ...etc all on the go, but I don't think you would want that, because in that case even a 4 GB card won’t be enough.
Now regarding SNES, I am not that heavy SNESer, but I can tell you the following: It is fully playable for games that don't have a special chip, but it is not perfect.
Now NeoGeo is worth the effort you are putting to set it up, I am not sure if you noticed but Shikaku has a FAQ in his signature that is truly useful.
Don't get disappointed by NES, it is fully playable on the GP32 and this implies it will be so on GP2X, the only problem is that no developer had put time on enhancing the port that was already made for it, so NES is absolutely possible but you will just have to wait for the saviour developer for Nintendo's beloved 8 bit console.
Again do not ignore the homebrew scene, it has many great games, and don't forget that beside emulators, you can use virtual machines and interpreters to play first person shooter games like doom and quake, great games like Ultima, and most importantly, point and click adventures using Scumm-vm.
Finally, if you needed any more help, do not hesitate TO READ THE READ ME FILES that come with the emulators
after that you can ask here and everyone will be more than glad to help (some of us here admit that they spend on this board more than they spend with their GP2Xs
), welcome to the community dochuge.