I'm gonna tell you how I would play this hand.

PREFLOP: Same as you

FLOP: I would bet out the flop, and just call the MP3's flop raise. I'm just calling becuz my hand is not that strong on this board, it is really important to me to see that a heart doesnt hit 4th street before I make another strategic move. If I had the King of hearts I would 3 bet the flop. I realize that just calling the flop raise is contraversial since I allow the MP1 guy to stay in the hand for one more small bet, but thats how I would play the flop.

TURN: Given that turn blank, I would spring back to life and bet out the turn. Partially for value and partially to protect my hand the times it is still good. I would not checkraise the turn since I do not want to get 3 bet on this board, and I would not check/call the turn since that line will not put any pressure on the MP1 guy. If MP3 raises my turn donkbet I would just call.

RIVER: I would check and call.