I'm not sure what Adventure Game Studio is, but if you're talking about AGI Studio, that uses a language similar to C. If that's what you're using, you might want to try GameBoy development. There's a complete development kit for that (GBDK) that uses a C-like language. It might be easier for you. Even assembly stuff on the GameBoy is a little easier than NES programming. I started with GB programming before I did anything for the NES.

Learning 6502 isn't the hard part, it's all the little intricacies of the NES (especially the PPU) that give people problems. But there's enough info on this site alone to get past this. You won't have to "discover" the vector table by accident like I did. :)

I don't have an address on hand for GBDK, but I'm sure you can find it fairly easily.

"There is a loud SAKRAHAH! and everything turns chartreuse."