General Questions (Stakes, River Scared and Learning)

Recently delved into cash games after playing STT's for a few months. My poker knowledge is pretty good theory wise, but when it comes to impliment it, i'm not so good. Anyway I have a few questions:
What stakes should I be playing? I usually play 5NL with $12.50 buyin when I 4-5 table and have about 3k hands. My win-rate is ok but I feel I have been running pretty good. 50 - 100k hands is a better guide anyway, so I think sticking with 5NL is fine, but does anyone thing moving to 10NL is better? If so why?

I'm pretty river scared IMO, how can I overcome this?
By river scared I mean don't like calling big bets OTR without the nuts. I always think of what beats me. How can I develop so a stage where I can be more aggressive and call bigger bets on the river with a marginal (but still very decent) hand?

PokerStars Converter Tool from FlopTurnRiver.com

MP1 ($1)
MP2 ($2.11)
MP3 ($0.84)
CO ($1.85)
Hero (Button) ($5.26)
SB ($4)
BB ($2.93)
UTG ($3.06)
UTG+1 ($2.18)

Preflop: Hero is Button with 9, 8
1 fold, UTG+1 bets $0.06, 4 folds, Hero calls $0.06, 1 fold, BB calls $0.04

Flop: ($0.19) 7, 2, 5 (3 players)
BB checks, UTG+1 bets $0.06, Hero calls $0.06, 1 fold

Turn: ($0.31) 6 (2 players)
UTG+1 bets $0.10, Hero raises to $0.31, UTG+1 calls $0.21

River: ($0.93) 6 (2 players)
UTG+1 bets $0.22, Hero calls $0.22

Total pot: $1.37 | Rake: $0.06

For example I have almost the nuts (I wasn't scared of flush.. it was unlikely and would have been played differently anyway), but the pairing scared me and thought he might have a boat if he had a set earlier, hence only the call.
I don't wanna start re-raising loosly or something etc and get myself into marginal situations because I'm not confident in my ability.

Finally how can I improve my game? I think i'm at a stage where I know the basics and intermediate theories well and hand strengths (eg nooby online article sites won't help, however Cardrunners videos seem pretty cool) but I want to develop my overall game. What books are recomended?

Sorry if it's tl;dr post just ranting to myself really (i'm sure most people go through this stage of their poker life).

For starters, if a guy hit a FH and you called on the flop and turn he would bet the river a lot higher.

And what do you mean by "I usually play 5NL with $12.50 buyin" ?

Mainly its just studying. Look at the betting patterns of the people who had monsters when you called and look at the betting patterns of the people who had a marginal hand when you called. You should notice a few things that are a little different and that will help show you were you should be re-raising/folding/just calling.
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Also...if you have these kind of questions and are questioning your ability, then 5NL is probably perfect for you.

On Stars they dont have 100bb max buyin games at 5nl, but they have 250bb max which is what he is playing.

OP why dont you play 10nl if you can play 250bb deep at 5nl?

Coz the standard of play at 5NL is a lot more beatable. But yeah, I play pokerstars 250BB deep. Also being scared money isn't +ev.

Anyone recommend any books or training sites that are decent but not well known?