There are only 4 chests in the set so you can only get 20 for them, but with a cook you could get 3 maps for another 12. that makes a potential 32.
play the granny wata on 1st play will get a potential 12
play the freed slave on 2nd play will get a potential 15
playing the gambler on 3rd will get a potential 6, a payment of 2 for the tiles you would have picked up and the payoff of 8
playing the cook on 4th will get you 2 tiles , needed to get the full 32 treasure payoff.
playing the first mate on 5th will get you a potential 6
and playing bosun on 6th will get you 10
32 + 12 +15 + 6+ 6 +10 = 81.
I don't think a higher score can be obtained.