Yes, I'm a newb ;)
The first question is the topic
I also want to know how you can have the same battlers/characters in different time zones (past, future), with different looks too...
For the first question, yes, it's possible. If you want a 3 player menu, you need to edit some scripts to make that, but if you just want to start with 3, you can edit that in the database.
2nd question: Also possible, if you know spriting, you can easy change the age of the characters with no problem.