60 sounds like a good number to me (5 player teams), but I'm not 100% sure if we can get that many active players with enough upped cards. 48 might be better.
Well, I suppose the easiest way would be to look at current war teams, now many from each team could participate. Since I'm on team earth, I'll use them as an example.
Terroking: I'm sure he has plenty of upped cards.
Demagog: Again, I'd be surprised if he doesn't have enough.
Coinich: As a previous master, I would, again, assume he has enough.
Legit: Well, his forum account doesn't have a mega-amount of posts, but if Pervepic is anything to go by, that doesn't mean much. I really have no idea.
$$$man: Well, I think he would have more than enough if he hadn't been banned so many times....(you should really quit that, $$$man), so I guess it just depends on the specific day.
I think I can speak for dreggs, Timer, and Sky when I say we are a ways away, yet. I guess it just depends on if you do decide to make fully upped a requirement.