Hey taifoon,
nice hand, well played.
About the raise size, 5BB would as well be completely fine, because there is only one limper. In the AQ hand you mentioned above, there is one limper and SB opencompleter which counts as 2 limpers and therefore I suggested 6BB raise as I don't think one should raise less than 4BB +1BB per limper when playing OOP, make the villains pay to see the flop. But adding additional 1BB purely for playing OOP is not necessary nor bad, it just depends on your decision and playstyle.
Regards,
burek2000