I feel like I played this badly in several spots, because I didn't know how to properly analyze the situation. I'd really appreciate thoughts on how to size bets properly, and also thinking about possible ranges.

Oaks 2-3-5nl
Hero is in hijack with 5 5 and $550
Other stacks range from $150-$800
Villain in BB with about $500
4 limpers to Hero, who makes it $20
Button folds, SB folds, everyone else calls.
Pot is $120
Flop:
8 9 j
Everyone checks to Hero, and I take the free card.
Turn is 5
Checked around to me again. I have no idea where I'm at, but I bet $80.
BB calls, everyone else folds, and we see the river heads-up.
Pot is $280
River is 9
Villain bets $100
Hero?

What do you figure villain's range to be? I feel like most 2-pair hands would have bet that flop, so this is a straight, a 9 or a bluff with a missed draw. I feel like I have to raise this, but not sure whether to shove, or min raise. But mostly I'm looking for how I should be thinking.

There's only a few hands that beat you with your FH; 8/9, 9/j.

Could the BB have them? Sure, but it's pretty slim.

Shove put the V all in.

you want to make it bigger pre. the easiest rule of thumb is (4+ 1 per limper)xBB, although at least at $1/$2 it seems like you want to bet a bit more. so id probaboy make it $40 here. im sure some would argue thats too high, but $20 is def too low.

flop, well played with 6 in.
turn, i guess you bet, and good sizing, but six handed youre probably folding to a raise unless you have odds to call to a 10 outer.

river instaship. he isnt all that likely to be betting 1/3rd pot with the nuts, so more than likely id put him on a straight.

OP - Like Tomark said, you need to make it bigger so it stays fairly consistent with your other raises. Make it what you would make it if you had AA.

The flop is debatable - totally depends on what you would do with an over pair, two pair, straight, etc

The turn is fine. I highly doubt anyone puts you on a set.

On the river, there are a few scenarios to consider:
1. BB is taking a stab at the pot because you checked the flop, bet a blank on the turn, and now he should feel like he can steal it. He won't call a raise unless you think he thinks you can bluff, so just call.

2. BB flopped the nuts and is slow playing it hoping you'll catch an A. In that case, he'll call your push because your boat is hidden.

3. BB flopped 2 pair with 9x and now has a boat and is value betting hoping you have something that can call.

4. BB flopped a draw with Q9 or T9 and is value betting hoping you have an over pair. In that case, he'll call your push because your boat is hidden.

The thing is, if BB has two pair, you could make the case he wanted to check/raise the flop and missed when you checked behind, but then why didn't he do it on turn? So I don't think he has two pair on the turn, but is more likely to have something like T9 (or A9).

Now the river hits and BB's got trips and BB thinks BB should be good so BB's betting for value and I think BB will call a shove because (a) the only hand he could put you on that *might* play this way is JJ/99/88 (or A9), but he has a 99, so it would only be JJ/88, (b) you still checked that "dangerous" flop instead of betting when there are at least 12 cards that could come and beat so you are even less likely to have JJ/88, so (c) your big river bet is most likely a bluff with AK.

So I like you making an all-in raise. If he flopped a set or two pair and has a bigger boat, that sucks, but that's poker.

Cool spot. Raise, but not too much given that anything he has that somehow beats you here has been played in such MUBsy fashion (other than 89) that you can too easily blast him off trips and even some slow played straights. His $100 riv bet looks more like a safe value bet without the nuts more than anything else and should still include 9xxc/9T once he takes a turn ck-c/riv betting line.. Even though MUBsy, he's still going to bet some of those hands when the BDFD misses and he feels more confident with no cards left to hurt him. Still some straights terrified of making the pot big counter intuitively because of the FD (67/QT) make up the rest and he can bet those too now. He has some 89 in there of course, but he probably just bet-c that anyway on the riv so that's not enough of his bet-c range to justify flatting his 100. If you shove, he likely only calls 89.

Raising pre will probably never be wrong, but I would take the cheap flop here especially with so many limpers in front.

Flop is fine. No set, no bet. Not sure why you don't know where you're at OTT when everyone checks to you. Good bet and size.

Raise river. How can anyone put you on a boat? You look more like AK with your line. V could have Jx, 9x or even be block betting 8x. I would be extremely surprised if he checked again with a straight, set or J9/98 OTT and just called your bet. Go for value and reap the rewards of having raised 55 pre.

V ck-c 80, donked 100 otr. He always has >1p.

Given that our line looks AKish and V donked just $100 into $280 OTR, I'm not convinced he always has better than 1P. I can see A8 or Jx block betting.