I'll play whatever rules, but the standard starting format is: 1x QB, 3x WR, 2x RB, 1x TE, 1x K, 1x DEF and then a bench. Pretty close to what we already do with 2x WR.
Adding a flex on top of that will eat up the free agency with this many teams. It's usually stretched pretty thin as it is.
All for keeping it PPR though as it's the only PPR league I get to play in every year, haha.