1/2 NL Texas Holdem full table
The Hero at SB with AK off suite ($240 behind). NIT player raised at BT to $12 after 6 players placed blinds ($200 behind). I decided flat SB and just called. BB called too ($300 behind). BB player was playing 75% of his hands, got involved after the flop three times: ones betting and chasing gutter, second time betting with ace without kicker, third time had monster and slow played it.This time BB called $12. MP1 called $12 ($350 behind), MP1 was calling 90% of the hands and playing small ball. So 4 players in the hand and we are going to flop: 4, A, 8 all rainbow. Hero at SB checked, BB checked, MP1 bet $12 into $58 pot. Original raiser at BT folds. Hero calls $12. BB re-raise to $30. MP1 folds. SB with TPTK calls. Pot: $130
Turn: J , board is rainbow SB checked, BB raised $30, SB called $30 Pot: $190
River is blank. SB checked, BB raised $50.
Your thoughts?

I would recommend a 3-bet pre to around 45-50 to at least get this hand heads-up and maybe even take down all the dead money immediately. Even against a nit on the button AK is a solid 3 bet here. AK plays better heads-up.

As played, I would at least lead the flop for 25-35% pot for value through the field of limpers given the initial raiser was on the button and will likely be checking this flop. The board texture doesn't require a big bet here. However, you have turned a rather easily played hand into a difficult one by playing it out of position against many players. You have check-called two bets on the flop, another on the turn, and are now faced with calling $50 to win $240 on the river. I believe this should be a call at this point in the hand because you are at the top of your range as played correct?

As played river is OBVIOUS call as you underrepresented your hand alot.

Preflop having such a fish on the BB I would also consider just flatting, but 3betting is also good.

I might also raise flop as the bet is SO small, like trying to buy a cheap turn card.

I did call $50 on the river because my hand was underrepresented, but I somehow felt that it was more of the crying call. The Villain shows big blind special: 4, 8 off suite which he calls $12 raise pre-flop.

You got to squeeze raise from the SB with AK. Hell,.. not just squeeze but take the pot down right now preflop and get it over with. You got the best hand. Why limp with a monster that doesn't even need to hit the board in order to make a profit. You always got a free roll with AK if you play it aggressive (if they fold, you WIN, if they call you still make TP and WIN by the river. Only six combos 3xAA and 3xKK out of 1326 are better. The rest 1320 are all dogs to AK.

One more important thing:
You say: "NIT player raised at BT to $12 after 6 players"
Well, if the NIT raise 1bb per each player he's a donkey too. The real raise in 1-2 game after 6 players are in should be $20. The $10 is the standard raise as the 1st one in and 1bb+ added per each limper. I would even make it $30+ OTB. But you should 3! his Mikey-Mouse $12 to $36 right now and take your pot down. It belongs to you by right.

If you play AK in a multi-way pot with 6 other players, you got 24.3% equity. If you try to squeeze but windup playing heads-up you got 65.3% equity. Almost 3x more equity.

This is a good opportunity to practice, execute and playing 3! pots. Try it, you'll like it and sooner you'll be 3! with A5s or ATs too.