Hi,
Villain is unk, I had only 4 hands on him. I am betting flop and turn to get value with top pairs since he will be calling up to 1/2 pot. However, this line seems also reasonable for a flush draw, which is completed OTR. Should I bet there or just x/f?

pre is okay, so is open folding

Flop is good. Can make it a little more. It's one of those flops that they are either going to like it or not.

Turn is fine.

Horrible river card. I'm never betting there. Probably check/calling.

Yeah, I need to pay more attention to board structure and whether V likes it or not.

What sizing do you call OTR after x? Only up to 1/2 the pot or even pot but no AI from V?

pre is kind of meh, but not too bad
everything else is fine, but like fidstar stated really bad river card. i would be check calling before i was ever betting river. and check folding more likely

fold pre

+1 to fold pre, In a .50 game you can prob. justify some different plays but its good to get into good habits and opening this hand from EP is gonna be marginal at best.

Preflop with 6 players to act after me I fold QJo for sure.

I don't mind half-pot on the flop as a standard bet-size when you are multitabling. On the turn though you have 433 in the pot and effective stacks of 1306 for almost exactly an SPR of 3. You should at this point be sizing as if to get it in (with value and bluffs) so maybe you could be 3/4 pot now, and go for 90% pot on the river. As a rough guide, in HU pots you need to have 1/3 of your original stack in after the turn betting to make a pot sized river shove, so in this case try to make your bets add up to about 500.

Against an unknown in a 50c game I would definitely check-fold this river - it's a scary card for him and he's looking more at his hand and all the stuff that has overtaken it rather than turning second pair no kicker into a bluff. If we're good he'll check behind and we take down the pot. If we're not he'll tell us by betting and we fold.

EDIT: TBH I would probably fold this against a known or good player too. I just don't see what bluffs he arrives here with and it's rare they turn weak showdown value into bluffs.