Dude, I'm like one of the biggest digimon fans ever. If you need help with character ideas, ask me. For inspiration, you should play digimon world 3 (if you already haven't) It's a ps1 game, but the concept of playing online was included. Maybe that game would help a little. Oh, and you should definitely put hidden Mega level bosses randomly around the maps. That would really get someone. Lets say you got a level 12 kotemon and you run into a level 79 wargreymon. or even worse, omnimon. that would make you crap your pants.
ps- if you are gonna do it farm style, do a ABS instead of a turn based battle. If you can simulate the feel of Digimon rumble arena in a rpg, you would rock.