just jam the turn 

I think you are getting free rolled occasionally but not often enough to only call this turn. You also block a lot of the thin value hands like 88/77/Kings up that might do this for value so his range becomes more polarised to straights and big draws like 9TJ with spades and against that range I think your better off jamming the turn.

Jamming turn, its hard for your UTG range to have a lot of 56 combos (not to mention how many of them you're betting out on the flop vs 3other players) so he might be more aggro with draws.

river - bet smaller to induce rebluff - again hard for you to have nuts, and even harder for him to have made calling hand since you block 7&8 sets

If he's not continuing w/ his bluffs on brick rivers, your probably better off just jamming turn and realizing your freeroll equity the times you both have straights, or getting it ahead the times he has a massive combo draw, or just making him fold stuff w substantial equity that won't put more money in unimproved.   Also keep in mind if his strategy is to give up too much w/ his air, that opens up some interesting opportunities to float his ch/r's with significant bb's behind. 

For your range, I think calling turn is best and that's the like I'd generally lean towards taking. 

I think you should be raising turn some % of the time with your nuts and calling some % of the time. Given you have a redraw I think 3bet small is better for your overall range play. Do this with some other draws as well.

Thanks for the advice. Having thought it through, I think I like flatting turn as the best range play, and also because I think his strong combo draws CR flop, and I thought he could have some blocker bluffs on turn. I agree that betting smaller on river is better as there was plenty behind to induce rebluffs.