I haven't done a 2-QB league in a very long time. Problem I found with it was the league sizes; since you need a backup for bye weeks and there are 32 NFL teams, that means that there should be at the very most only ten teams (32 divided by 3 = 10.67). When there are 12 or more teams some teams end up taking zero points on the bye weeks, and that leads to owners quitting - which is never good for any league.
A 2-QB league intrigues me, but in my opinion it is best if the number of teams is limited to at most ten teams, and optimally to eight teams.
As far as joining a league now - it just seems way too soon. Unless it is with people you know (i.e., co-workers and/or friends) my history has been that when September rolls around you end up with some absentee owners and teams running on auto pilot - again, something that really stinks and you want to avoid.