There is some merit in checking 4 way against decent opponents on this flop but given the loose passive fish betting flop and turn is fine although I would go slightly large than half pot OTF.
Think given your small sizing on both flop and turn i would expect more marginal hands to be getting to the river JQ/KJ/A9s etc. so think bet folding half pot would be ok.
Yeah id agree that 2.50 is a little big, probably go for like 2 though. AQ is at the bottom of our value range, but still think we can get value from enough worse. Based on 75% c bet otf and ott, pot would be $6. I think 2 is fine, to get called by AX, K10, Q10, KJ, QJ, possibly even 10x.