gamingw only has Pokemon charset (but nothing else Pokemon). However they got pretty much rips from every single SNES RPG game (which is the primary resources for RM2K)
Battle System is hardcoded. You can't do anything about it, unless either....
a) "out of battle" battling. But this is almost nothing but "screwed up" as it's near impossible to do random battling. Plus every event will have like 900 pages attached to it since RM2K cannot perform calculations (no it's not a computer programming program like Visualbasic or Borland, so don't even try IF statements and etc)
b) some darn complex code beyond my knowledge... though i have seen games that have done that. However... they are the RM2K veterans who paint everything themselves, make battle animation themselves and etc... if what i know is like a candlelight, then what they know must be as bright as the great moonlight (no pun intended)
now regarding kecleon's questions...
Pokemon battle animation: it's exactly the same way how you manage normal battle animation. Just have to do it yourself. If you mean Pokemon battle animation that are exactly alike to the gameboy, then you are doing one of the following:
a) using the wrong program. If you're making your own Pokemon game, you should hack from the original one and transform it so much that it's like your own. We have a forum dedicated to hacking... check there
b) wasting too much time... RM2K is capable of better graphics compare to GBC and equal in power to GBA
There are NO pokemon faceset... so paint yourself?
Music files: i strongly suggest you NOT to do this. The only available Pokemon music out there are wav file (there are mp3s but RM2K do not support mp3 even with the so called "mp3 patch". That patch is a phoney unless they released a new version to fix it). And one wav file is big enough to double the size of your game... making it very hard to distribute. I have first hand experience to this problem for 22sa's game so... believe me. If you insist on doing so, play the game with roms and visualboyadvance emulator, and tehre will be a handy option to record the background music as a wav file. Import the wav file to RM2K and voila!
i believe i emailed you the only 4 pokemon chipset available already... there are some rare tutorials out there that will teach you how to rip chipsets too so you can learn it yourself and rip it yourself as well (imho, the 4 chipsets available now is completely insufficient to a game maker's needs)