Sorry, this group's mainly here for archival purposes! We're not accepting new members
No worries! :)
So sorry for the delay!
Fresh and In-training Digimon are unlocked along with a Rookie (whether it's the original partner or a purchased extra partner).
When you say characters from an existing franchise, do you mean, for example, a Pikachumon? If so, yes they are allowed (within reason: the art/designs must be your own, they must look/behave/evolve like a Digimon, and they must follow all the group rules).
Yep! You'll have to 'buy' them with the points you earn by doing pieces for the group, but if you have the points you can get as many as you'd like (canon or original).