[lapoker17]

You need to raise that flop - UTG limper could have a set here - you should not be slowplaying flushes in this spot (or really ever) - in this hand you obviously get all the money this way - in other hands you either shut out the set to avoid difficult situations later or get your money in when you are ahead - if he doesn't have a set or made flush (which is rare as how many spade hands are limping UTG when you hold the Ace) then he's not putting in any more money anyway.

Betting the river is a read thing - but I'm usually checking behind.