- I think in a vacuum I should 3bet this hand pre. Stats indicated low PFR, so I assumed his opening range is tight.

- No lead on turn, because I have showdown value. Correct? Wrong?

- River x/fold better if I stick to my assumption that he is passive overall?

A5o is a mixed 3bet/call in theory, vs a tight player I would tend to call more although sometimes they also fold too much vs 3bet, and then you can consider 3betting anyway. Beware those fancy solver 3bet from BB are very hard to play postflop (at least for not-so-great players like me) when called and you can easily spew a lot of chips...

On the turn you often have the best hand and you can get value from many holdings : Tx, 8x, straight draws (J, 9, 6,) etc. If they are passive they won't raise you with a bluff, you can comfortably bet/fold, this is a strong argument for betting in my opinion, and you can bet quite big also. And if they fold you are not too sad either.

As played I would x/f river yes, they rarely bluff and never value bet worse than A5 for this size.

Bet turn aye

Always calling river AP.

I’d flat wide here pre in general against most players- A5o is well within for me.

- I like 3betting or calling. Either is okay. PFR may be low, but BTN, SB usually are the 2 spots that actually pump that up so possible he's just tight in other positions.

-SDV more of a better idea OTR imo, there are still cards to come so what is SDV even mean OTT? I'd consider betting here, a few draws came in and while we have TP, it may be vulnerable. You don't have to go big and you can also x/c pretty comfortably OTR

Never folding river. This line isn't so strong most of the time so get comfortable calling these.

Many thanks for your feedback.

Not folding after taking this line. He could be value betting Tx

If he is opening tighter you should defend tighter, maybe he opens BU 27% which is CO open range in that case you defend like you would vs CO. Most likely this is fold pre.
AP-If he is passive, then you want to bet. He wont bluff much or bet thin so there is no point in checking and hand is strong enough to put some money in.