Strategy vs. maniac in very deep HUNL cash: 1/2 NL, 250-1500bb deep is the standard stack depth, average 500bb.

Preflop:

Villain Characteristics in BB
⦁ 4x 3betting ~35% pre vs a 4x open
⦁ Folding ~15% vs a 4x open
⦁ 4x over a button limp close to 100%

Villain characteristics on button
⦁ Opening ~90% of hands to 4x
⦁ Fold to 3bet 0%
⦁ 4Betting 4x depolarized and too many value hands (AJo, KQs, some oddball bluffs but these are not super frequent) - He is much more abc with his 4bet range than his 3bet range.

My Button strategy
⦁ Fold bottom 30% of hands
⦁ Limp hands in the 30-70% range with intention of calling 100% of his 4x raises. (I am doing this because otherwise I would have to fold far too often to his 3bets, I do not have the option to 4bet bluff because he folds to 4! 0% and calls down very light too often)
⦁ Open top 30% to 4x
⦁ Fold to 3! 0%
⦁ 4Bet/Get it in with top 3% (QQ+, AK) (He plays so crazy in 3! pots there is a lot of value in simply calling 3!, then calling down, he will pot, pot, pot regularily with his bluffs) - If we are 500+bb deep this range will become KK and AA only. If we are 1000+bb deep this will be AA only.

My BB Strategy (He opens to 4x ~90% of the time)
⦁ Folding 65% (Is this too high/low?)
⦁ 3Betting top 10%
⦁ Playing relatively passively, postflop, c/r'ing strong hands on flop, calling down relatively light.

Postflop

⦁ Legitimately the most maniacle player I have ever played regularly heads up.
⦁ Bets flop pot, turn pot, river pot very, very frequently with a wide array of strong and weak holdings in a 3bet pot or single raised pot.
⦁ Calls down incredibly light in a ton of situations, I have had him call down pot, pot, pot with 3rd pair, he's called down pot, pot, all in in a 3! pot with ace high, etc.
⦁ His calldowns are not very calculated, he is very consistently calling down WAY too light, to the point where I have started cbet bluffing, 2 or 3 barrel bluffing with a close to 0% frequency and just value bet him very very thin.
⦁ Fairly polar on river, in odd spots I have called a pot sized bet into a 100bb pot on the river with a bluffcatcher and been good.

My Overall Strategy
⦁ Playing extremely exploitative strat vs this specific maniac
⦁ HE DOES NOT LIKE TO FOLD. Whether it is calling me down with 3rd pair in a 400+bb pot or barreling off far too often with bluffs, he does not like folding. I plan on bleeding red line to this guy and crushing him with showdown winnings. (Especially since we are very very deep and he makes a lot of mistakes based on stack depth.
⦁ Have a stronger starting hand range pre, a better constructed 3bet and 4bet range, let him barrel off postflop, value bet relentlessly thin.

Questions
⦁ Should I explore playing even tighter from the button, with a 5-6x open size with top x% of hands?
⦁ Is my limp/calling strategy with the middle of my range to combat far too frequent 3! and his 0% fold to 4bet sound?
⦁ Is my 4! range bad? Should I be 4! TT, JJ, AQ, as well even if we're 500+bb deep and folding to a 5!? At what stack depth does stacking off with QQ and AK become really bad even vs a maniac? Is folding KK to a 5! ever an option no matter stack depth vs a maniac? (think 1000bb deep?)
⦁ Since he is raising over limps near 100%, would it be more profitable to limp ~99+/ATs+ with the intention of reraising?

I typically do not deviate from what I understand to be a relatively balanced strategy for heads up, but there are so many obvious exploits here, and I truly do not believe Villain will adjust well to them, so I am trying to maximize my winrate vs. this specific opponent. If he makes any drastic changes, I can always resort back to a balanced strategy and be a moderate winner. I'm trying to crush this opponent for 50bb/100.

Any advice is greatly appreciated. Thanks.