wp!

I think QQ is a 3b pre but I don't mind flatting too. I think if he has AA/KK he will check back a lot this river considering that he needs to fold a very large part of the time a x/r river shove. Also, checking twice let his c-betting range (which is pretty wide on this stakes I think) keep wide enough to let him use his bluffing range. 

I rather play a bigger pot with premiums in this 100bb deep games but being balanced about it is also good. 

I'm almost never 3b/f QQ against an unknown and even JJ against some players lol. I don't play this tables anymore but assuming that UTG range is that narrow, 5.1% I think it isn't that reasonable assumption and also that Axx, Kxx boards appear that often. If he has AK, that is the probably the only non pair hand that he may continue, he's already blocking more than 20% the probablity of an Axx/Kxx board. 

If you never 3b as bluff of 3b some thin value you are unbalanced in this spot and people can exploit you a lot here. You can check your stats but I don't think people are folding that much to 3bets from UTG but I don't have a sample in NL10 to tell you. 

Not a fan of 3betting vs such a player (ep looks nitty), ep - bb just not gonna work out well with no dynamic/history. little deeper too..

I think a 3bet here is too thin for value preflop. That doesn't necessarily mean you are unbalanced in your 3betting range preflop, it just means that you are choosing to 3bet tighter both for value and as a bluff due to the opener's position and overall nitty stats. If you do choose to 3bet and get 4bet vs anyone running 15/14 opening from UTG at 10NL then you are in a very shitty spot and to be honest I think folding is almost certainly the best option. You would be lucky if their range was any wider than QQ+. If they have a 4bet bluffing range at all in any position it is almost certainly restricted to late position dynamics.

I think the best line on each street was what OP chose to do as played. Probably check/calling river except against an unusually large sizing.