well, about asm, it has taken much of my time, and if you know what each command do already, then you're already prepared to do what you want. You just need to use the right tools and know the offsets (which you're gonna discover with the right tools), and by right tools i mean a decent disassembler like VBASDLH or NO$GBA DEBUG.
I'm not into rom hacking nor ASM much nowadays, so i'm not in the mood for teaching, but let's give it a test run.
Give me some idea you want to make using ASM and i'll see if i can do it, and if i can, i will explain it step-by-step to you.
(a easy thing would be better!)