Aw, thank you! Alot of the sprites I do are based off original trainer sprites in the Pokemon games. I use the originals as a base, and then do all my edits in Paint. The one in my profile pic in particular was based off Whitney's sprite in Black 2/White 2. You can find the trainer sprites from the Pokemon games at The Spriters Resource (link). As for hints on drawing and colouring, um, just keep practicing! I've been doing this myself for a while now, so I've had lots of practice :D Another good idea is just to roam around the Pixel Art forums here and just see how other people do their sprites.
As I said, it's a wonderful idea. I always loved the Personality assessment in PMD and always wanted it to be incorporated in the main Pokemon games. It'd really make the game feel much more personal and unique. Good luck in making it work!