A7s flush - bet sizing?

With nuts you generally want to build a big pot and get the stacks in by the river, not slowplay.

Your opponent either has a) nothing and he is going to fold anyways b) a made hand and wants money to go into the pot as to protect against you drawing out on him or c) has a draw, most likely a high diamond, and is hoping to make the flush. In any case, betting large should be your best option. It gives you the most value. a) will fold, b) will reraise and c) will chase value that isn't there. I'd bet about 3/4th of the pot to give c) a chance to call.

We need to bet big on all streets.
With these hands we want to win huge pots. We divide our stack so we are all in on river and we go go.
remember: BIG POTS BIG HANDS

If he folds then that is it. But if he calls small bets and we see river and he has a good hand then we slap ourself.

I think this is standard call preflop. We are bluff 3betting some small offsuit aces. As played, I think it's no time for slowplaying because we need to get value when have the nuts and he still might catch up a fullhouse on the turn/river in some cases.

Standard call preflop. Postflop you must bet and try to take value. If villain wants to stay you have to make him pay while you are ahead. And of course you do not want rhe board to pair.