Throwing ideas back and forth with Jay over messenger I'm throwing my hat into the 2 levels as a time bin. Since even and odd levels give different bonuses it would actually be pretty clean: 1 feat, 1 power, +1 everything at each level up. I'd still lean towards once a month, since realistically I'd expect to get 3 sessions out of a month. But it's less book-keeping than needing to level every other session and I think balancing magic items may be easier.