Preflop, if be honest i think the best is fold, but obviously 3 bet is fine too, if they will fold enough. I would cbet this flop. Sizing 2/3 of pot.

Preflop, this is a bit too loose to 3-bet. I would start 3-betting 66+, but 55 might be fine. With 55, maybe mix in a 3-bet 50% or 25% of the time and fold the rest of the time.

As played, either c-bet flop or check/raise. You can also check/raise turn.

A set is a very strong hand, and you don't want to slowplay. Especially if you have bottom set, you don't block top pair, so you can often stack Villain if you play it fast. Slowplaying top set is ok.

On the river, his range can be wider than what you outlined. He can have KQ and JTs. Maybe Q8s as well.

I would probably not fold a set. You only need about 35% equity to call, and he should have plenty of two pairs in his range.

The 3 bet size could be bigger as your OOP would 3 bet a bit larger to 3.5-4x you want to make his odds worse then 1:3 as you want folds and people tend to call lighter in position.

The villain had QQ.

I would expect his 3b calling range to be something like TT-66, maybe JJ for his pair range, some KQ, KJ, KT, QJ, QT, JT and some suited Aces and like AQo. While 3 betting 55 is far from a disaster (I do this sometimes with 66 and 55 since recs will call with 55-22 in this spot and you can set over set them on occasion), I think A7s-A3s make better 3 bets in this spot. You can out flop a huge portion of his range (all his pairs) and you hold blockers to him having Ax. My range here vs CO and BTN is mostly linear in nature with a bit of bluffing coming from one or two PP's (on occasion, mostly when I feel I am running well. I eliminate them completely when I am running/playing poorly) and then A7s-A3.

As played, this is a great flop to be betting with your bluffs so you will need some value combos in your range here too. The top end of his calling range has a bunch of Qx in it so I think I would continue with c betting this flop.

If you choose the passive route, then calling down is fine here obviously.

First of all id want to know what CO RFI% and Fold to 3b% are (if I have any). I do not play 2nl but starting out with a value heavy 3b range would be my starting point. 55 seems a bit to weak as it rely on a decent amount of foldEq preflop.