You cant make a group with a free account. You can join one, but cant make them.
In my opinion, play PVE if you just wanna play around for awhile with out getting raped. If you wanna fight people, then you can always go to an arena. Or make two characters, one for PVE and one for PVP.
All the mentors are pretty much the same. You also end up doing missions for all the mentors throught the game. However, I found the jokers missions to be more entertaining then the others because you are in gotham.
Here
this might help. Also try the FAQs at the bottom of that page.
