I am not an expert but here is my opinion:

Do not raise the donk flop bet unless you want to bloat the pot with what is probably the worst hand at the moment. A call is fine with your two overs and a backdoor straight draw.

On the turn I think the call was fine, although a raise would be ok too. I like the call because he is betting like he has a weak pair from the flop.

On the river, a 2 is not changing anything, and you could think about raising for value here. The board is really good for your hand and I think he will call a small raise with a lot of hands that you have beat.

I prefer to stick with calling his donk bet vs a half stack.

I don't want to see him shove when he have potential to make a decent top pair hand as well as him shutting down and allowing us to take the pot away when he's doing this with Ax.

Turn is a horrible spot as I want to raise for value but would hate life if he jammed. I would probably just call him down over 3 streets as you did.

If you know that his frequency for those small flop bets then I don't mind floating overcards + backdoor in position, but vs. more conservative player folding would've been totally fine. I prefer calling to raising since villain might be inclined to bet on the cards that hit our hand.

On the turn I'd probably just raise for value to take control of the pot and possibly buy myself a free river card if I wanted to.

As played calling the river is fine. Raising might be a bit too thin at this point.