Aaaand here we go...
In order
-It is, but can lead to some severe bugs due to GBA roms limitations. Maybe try with NDS hacking or an RPG. Also, that would be a whole bunch of maps, and GBA roms arent infinite, nor are NDS roms.
-TCG??? It has its own game?
-There are only 13 or 15 (idk the exact number) tilesets, soooo nope.
-Space (tilesets, pokemon, maps, trainers, etcetcetc), new regions being added, etcetcetc
Again, try with RPG. More lag, but less limitations.