1. He has a straight, there`s no doubt about it. There are too many straight possibilities. All the sets and straights have you in pretty bad shape, you also block the clubs so this reduces the possibility for him having some kind of big combo draw with clubs. Only hands you beat are his bluffs with blockers, even two pair hands are 60-40 against you. He is pot commited so you dont benefit much, most of the times you just get your money in bad.
2. FOLD! You don`t want to make too many of those bluffcatches in PLO with just one pair on this kind of boards.

He has such a wide range hard to see him not having at least 2 pair by the river. He prob checks back his kxxx on the river, you block club draws, only hand u beat that makes sense is j8xx

What are your thoughts on checking the flop? Feel like this flop isnt great for your 3bet range pre.

Didnt do the math but it seams like you have enough equity to shove the turn, if correct then saves your from making incorrect folds on the river

I can't see what you trying to achive by betting 1\3 PSB OTF. I like the play OTT and OTR.

don't know what is right - I would go by x\decide OTF. often x\fold