1). No GBA RAM
2). NOO GBA mode to use the GBA ROM in the DS for Multiboot GBA like the GBAMP does.
3). It would actually be possible if you had a EZFLash 3-in-1 or w/e.
The other main bunch (m3, G6 and EZFlash) only struggle with classic nes/famicom mini (use an emulator like nesDS, pocketnes or HVCA) and a few ones that need patching (boktai, pokemon RTC, warioware twisted...).
There are loads of what GBA cart to get threads with lots of discussion as well.
The Greek dub of Toy Story's You've got a friend in me is still a classic even among boomers who've never watched the movie, mostly because it was sung by a famous beloved Greek singer