Lets say btn is a good reg.
what are good flops to c/r generally with air?

I tought that like K54 with two cards of the same suit is good (two low cards), because if BTN don't has KQ+ here it is super hard for him to call, and i at the same time could easily have a flush/kombodraw/set.
But then again i don't seem to get the credit i tought i would get in these spots and i get re-raised again :O

And i think ace high board with two low cards is even better because he will fold like 78s-KQs, and 66-maybe even KK because we rep flushdraws, twopairs etc that wan't to get it in against AK.

I don't know :P

Depends on your defending ranges, 3bet ranges etc.
Vs regs who used to fold to a lot of 3bets I used to 3bet a lot of trash and flat AA,KK,QQ etc. So it means you can have a pretty wide c/r range cos you have so many more nutted hands. So on a flop of say 2c5c9h I'd use all fd's,gutshot bdfd's,2 decent overs +bdfd,AA,KK,QQ etc,A9. Then continue barreling on cards which increase our equity or are scare cards, 6c for this example.
So if we c/r KhQh on this boards barrel any h,c,A,K,Q,J,T.
Meh im just rambling here, it's player dependent, but just be a bit creative in your ranges and make sure you keep it balanced. You wanna c/r vs players who cbet too much and if your flatting premiums donking if they don't cbet a lot. Obv if they're never folding to 3bets then we're not gunna have much of a c/r range cos we'll be 3betting them with big hands.

This is pretty badly explained, HH examples would be better.

Boards where you raise a lot of hands for value (balanced approach)
Boards where villain has a lot of air (exploitative approach)