Put simply, there's no definitive template for battlers, it's all limited really on if you wanna have all the battlers follow the same art style. A lot of mine are modified from game artwork, with a few having been drawn by a friend I'm commissioning (these being final designs for the creatures that will be carried on to the final).
Anyways, if you're planning to work with humans, pick yourself up a copy of Daz3D, it works really well and the software itself is free + a lot of the models are free, though if you don't give a damn about legality, you could use BitTorrent or Limewire or w/e to get the various models.
Depending on art styles, I reccomend the following:
Anime:
Aiko (Female)
Hiro (Male)
Realistic:
Victoria (Female)
...it's been way too long, I forgot the name of the male default that usually comes with it.
For monsters, go pick yourself up a sketch pad or an artbook for a game like Dark Cloud and start taking notes =D.