Another good spot to 2 barrell is if a Q/K/A hits on the turn, as long as you have a "reasonable" image.

And I've noticed sometiems c betting a low flop like 7 5 2 rainbow is bad when you have a loose passive and have cbet a lot - they will call with over cards or any pair then somteims bluff on the river. But if you wait til the turn, they fold more, especially if you've checked behind with good hands on the flop as well.

I dunno about the river thing, 2 seems like a reasonable AF but it comes down to if you make enough value/block bets against passives I think.