Hello jules97,
Preflop: Fold? Why would you ever consider calling here vs unknown???
As played
Postflop: Why do you donk???

Answer me this questions first?!
2) Second question, Let's say things are switched up and hero is BB and Villain opens 4BB from UTG @ 8% PFR from UTG. Hero has AJ (or AQ) and doesn't want to 3bet. Should hero fold?
Whatever hero feels being the best, I can't say to you what to do cause depends highly on your postflop skill, understanding the opponent and etc.

All 3 options are possible: 1) raise ; 2) call ; 3) fold.
3) In this second scenario if hero is BUT instead of BB should he fold too? or call? I found myself in positions like this with AJ or AQ and I don't really want to fold them, but I am scared of getting into a hand dominated and getting burnt. I suppose I should just be folding these hands, especially if OOP?
Again, everything is possible.

There is no default line to follow. Poker isn't that easy as you imagine it being, the chart what you have seen so far is just a guide how you could play according it. But it's not a strict follow line. The better you get the more you will understand the game and will even discard the chart and never use it again.
Best Regards.