I like the way you played flop and turn, although I agree you could go bigger on the flop.

As you’ve correctly pointed out, a fish’s range is likely to be inelastic, which allows us to bet exploitatively big with value and size down when we’re bluffing. I’d go closer to 3/4 pot here and expect the fish’s range not to contract at all.

I like the turn play. We can defo get called by worse hands vs this player type.

I agree with your river thought process and think either check/fold or bet/fold is the way to go.

Against a passive fish, I think check/calling isn’t a high EV line. They call wider than they bet, so we put money in against the stronger hands in his range by check/calling.

It’s thin, but I’d probably lean towards bet/folding about 1/2 pot. I think we can still get called by some 1-pair hands. Vs a raise it’s the easiest fold of our lives.

Overall I think you played the hand well and that your thought process is really sound.

Could the flop bet be bigger for value?

Turn bet is perfect.

River:
I would bet the closest to a quarter I can on the river so that I can still look at myself in the mirror the next morning, then fold to a raise

As played, I can't decide if the correct sequence of events is folding and then throwing up or throwing up and then folding.