99 set, straight completes on river

Bet smaller and fold.
You can make flop and turn bets bigger.

I would definitelly bet flop and turn bigger, close to pot. We can bet/fold the river imo. Agree with smaller sizing.

I would've played it about the same up to the river, where I'm checking and calling small/moderate bets and folding to bigger ones. When we bet here for this size, to me at least it screams "blocking bet". We need to bet because we think we can be called by worse (unless we're bluffing, which we're not doing here), not because we don't want villain to bet. OTR I don't see any hand that can call us, so effectively we're making it so he'll either raise us with a better hand (or as a bluff if he picks up on it being a blocker), possibly call with higher sets and straights that choose not to raise and fold everything else. If we check, however, we're leaving hands in his range that we can beat, such as two-pair. If we're going to put the amount in OTR that you did anyway, why not do so in a way that we can include hands in his range that we beat? The reason I'm folding to bigger bets and not smaller ones is because on this board, if he does over-value a hand like two-pair, he's most likely not going to bet very big with it for the same reason you didn't: it's a scary board, but he may talk himself into not wanting to miss out on any value and bet too thinly. Usually a bigger bet means the straight or a bluff, but in this particular hand it's very hard for him to have a hand that he turns into a bluff OTR. I really only see one-pair hands that include an 8, and I think most of those fold the turn, drawing to the low-end of the straight and facing a second barrel.

I would have played it the same but bet sizings need some adjustment as said above.

Yes, we should get more value from weaker hands on flop and turn.