Villain is a 26/3 with a low WTSD

Thoughts on preflop size?

I figured his flop calling range is Jx, 55, 77. On the turn I wasn't sure if betting would get him off his hand, so i just checked and tried to complete a draw. When the river makes the flush I decided to ship it since the draw completed and i dont think a 26/3 can handread well enough to realize i never have a flush here. Also with the flush completing AND the king on the turn I could get a fold from a jack. I don't think a set checks all three streets and it would at least go for some value on the river, so i discounted 55 and 77 from being a heavy part of his range

PokerStars No-Limit Hold'em, $0.50 BB (9 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

saw flop

MP1 ($25.20)
MP2 ($52.50)
MP3 ($107.95)
CO ($35.45)
Hero (Button) ($52.25)
SB ($45.65)
BB ($49)
UTG ($51.50)
UTG+1 ($87.75)

Preflop: Hero is Button with 6, 4
UTG bets $1.50, 2 folds, MP2 calls $1.50, MP3 calls $1.50, 1 fold, Hero raises to $7.50, 4 folds, MP3 calls $6

Flop: ($18.75) 5, 7, J (2 players)
MP3 checks, Hero bets $12.75, MP3 calls $12.75

Turn: ($44.25) K (2 players)
MP3 checks, Hero checks

River: ($44.25) 6 (2 players)
MP3 checks, Hero bets $32 (All-In)

Total pot: $44.25 | Rake: $2.15