Pre: I think that 38 hands is too small of a sample to make the assunction that he's a maniac. BTW i'm ok with this 4-bet.
FLOP: we can bet/decide (I'm a bit towards b/f), but ofc check back sounds good with this particular hand in position.
Turn I like a check, knowing that we have medium SV and a medium draw - a perfect hand to check back, in my opinion. Give me a 9 instead of the 7 and I'm ready to b/c. Still, I think that it's too soon in the match to b/c profitably here, seeing that it's a rainbow board and his bluffs (if he's c/r as a bluff, ofc...) should be A54x, 654x, AQTx, maybe QT9x. Everytime the "x" is a good card (like a pair or additional draw) our equity goes down. Maybe we can find better spot to make a stand this deep.
River is whatever, if u think that he's bluffing OTT.

4Bing this hand is a significant mistake. We do push a slight amount of equity against some 50% ranges, but when we compare the EV of a 4B to the EV of a call (which we all agree has to be quite high), we also have to factor in the times we face a 5B. Even if it's relatively rare, the penalty will be severe.

OTF, I think there will be a strong emphasis placed on holding AKxx when cbetting bare TP hands so a check back is likely good.

OTT, we now begin to dominate a significant number of hands that can call us (though we don't know anything about his turn probe strategy) or x/r bluff us so I'm happy to bet and call.

OTR I probably call as well. I suspect that many players will not valuebet as thinly as they need to here which actually skews them towards bluffs

@reStacks What hands would you be opt to 4bet in this spot that could comfortably call 5bets or have high equity edge in those bigger pots. I'm a little new to PLO, the obvious candidate is AAxx ds and single suited I suppose but what other hands, If I had to pick some I guess I would use strong connected ds however they don't come around that often, so I guess ds Axxx with some wheel draws. nut straights?

Your question is a good and important one. I can't say I have deeply studied 250bb+ PLO yet, but here's what I can say:

Hands like A987ds as you mentioned have both a blocker as well as an overcard to a number of his value hands so I could consider using those. I would consider extending my value range from the top downward by adding more AKK/AQQ and maybe even AJJ. I would also add AKxx hands as well. It's true that these hands are unhappy when facing a 5B, however I think holding the Ace should reduce the frequency with which that happens and ensure that when your 4B is called (which will be an extremely high EV scenario for you and one that should happen way more than you being 5B), you will often be dominating him.