Answer to your first question is we can bet turn as a bluff. We would want to bet because UTG could easily have 2 pairs and sets in his flop leading range and when he checks turn he is often capped and cannot have many straights. When we bet the turn we allow ourselves to have the very top of our range (which is 58xx and 35xx) and if villain calls turn this opens up barrelling opportunities on non flush and non-paired rivers and often bluff him off any non straight hands.

IF we do decide to take the line above Hero should barrel river almost pot size on river to polarise our range.

I do like your idea to valuebet half pot or even smaller on this river to try and get value from any lower 2 pairs that decided to be sticky on the turn.