The first mistake was the bet sizing pre flop, has to be much bigger than .65cs after 3 people put money in the pot, close to 90c-$1.

Flop I'd go and make it bigger, $1.50, yes we have a lock on the hand but so many worse hands are calling, it's very drawy heavy and it makes our turn move simple (shoving).

As played I think the turn and river are played fine.

Yeah when your squeezing just hit the 'Pot' button as a short hand. It would have seen you right there.

As played yeah the sizing looks way too small. Loads of Tx, some Jx, FD's, SD's, even some overpairs. All will continue and you are going to hate quite a lot of turns if you get raised having kept everyone in the pot with a tiny sizing.

The biggest problem with this hand is sizing. You have to go a lot bigger both preflop and on the flop.

As played you kinda have to slow down on the turn given the multiway pot and one of the worse cards in the deck for you. Once the turn goes checked around you're definitely strong enough to go for a thin value bet.

I'll echo the other's thoughts on sizing. Way too small.

Not sure I can agree with a turn check though. The flush card is obviously not a positive thing, but surely betting for value is better than allowing somebody to free roll a spade. At 5NL you're still quite likely to get called by any pair with a spade even if you shove.

If you had have made bigger sizings pre and on the flop it would be a much easier shove even on this turn card.

You saying you would shove the turn even if its 3 spades on the board?
Agree with the size on the flop.

By making it larger pre flop and betting a larger amount on the flop you'd have most your chips in that you couldn't fold the river regardless of the card.

Yeh I agree with Harvie that if we have made it larger both pre and on the flop then it makes our turn decision very easy regardless of the card that falls on the turn. We will already have succeeded in our goal of forcing the villain to pay an incorrect price so if they have drawn out on us then so be it, we still have a decent number of redraws out to a full house.

Lets put it into practice for the hand:
Lets say preflop we make it 80c and we get the same number of callers, the pot will be ~2.40+ and we have just over $5 behind. Now we bet 75% pot - $1.80. Villain is not getting going to be getting the right price to call here with a naked flush draw at this point. If we get a single caller here then we will have ~$3.30 behind and pot is going to be over $4, if both players call it's going to be close to $6 so we are just always going to get our money in. They key here though is that we forced villains to put in a lot of money as a serious underdog so our EV with this line will be immense. One last point - It's also possible that villain has a lower set/some other type of value hand where he can put a lot of money in and is drawing almost dead here.

With the bigger sizings and as played, yes.

UTG+1 shouldn't have a lot of flush draws in his range calling OOP in a squeezed pot with no other callers so far, and the BTN has less than 80bb so we shouldn't be worried about him. There's still straight draws out there as well, plus all the other worse hands which might not fold.

One option is to maybe bet small enough to get some value and protection from a bare spade, but big enough to price ourself in if we get shoved on. Not sure which is best TBH as I wouldn't have reached the turn with so much money left behind anyway.

I probably would not squeeze with this many players in the pot. Won't have a lot of fold-equity and the hand will typically not play super great OOP against a bunch of guys. Anyway, raising is ok in theory, but sizing should obviously be a lot larger. We should adjust our sizing based on the number of players in the pot. Anyway overcalling is a lot more straight-forward even though both calling/squeezing have merits.

As played it's a good idea to underbet the turn in order not to give anything for free.

As played you made a correct value-bet on the river.