What would you do? #3 - Another two for the price of one

Two hands from my first multi tabling experience at $50NL. Within the first 30 hands, two really interesting hands came up, which make me really question whether I'm in over my head here... This was the ~15th hand so no real reads on anyone...

Full Tilt Poker $0.25/$0.50 No Limit Hold'em - 9 players - http://www.thehandconverter.com/hands/263050
The Official DeucesCracked.com Hand History Converter

MP1: $21.90
MP2: $55.50
CO: $30.00
BTN: $39.20
SB: $54.70
BB: $52.25
UTG: $16.35
UTG+1: $13.55
Hero (UTG+2): $80.55

Pre Flop: ($0.75) Hero is UTG+2 with Ac Ah
2 folds, Hero raises to $1.50, 5 folds, BB calls $1
Standard (from $25NL at least) 3x raise.

Flop: ($3.25) Jh 7s 7h (2 players)
BB checks, Hero bets $2, BB calls $2
Heart draw, and I want value.

Turn: ($7.25) 6h (2 players)
BB bets $4.60, Hero calls $4.60
Now he's leading ~half pot? With a paired board and a completed 3 heart board... hmmm...

River: ($16.45) 5d (2 players)
BB bets $12, Hero calls $12
Is he representing a flush here? If so, is he leading so strong? I'm making a hero call, but this is a pretty aggressive bet that leads me to believe that he's trying to push me off of the hand.

Final Pot: $40.45
BB shows Qs Qd (two pair, Queens and Sevens)
Hero shows Ac Ah (two pair, Aces and Sevens)
Hero wins $38.45
(Rake: $2.00)
I thought for a long while about folding the river bet. Would you be calling here? I calculated that I'm roughly a coin flip ahead / behind. Either I'm shown a flush or boat, or I'm shown nothing. The additional question is: Is this guy a fish or is he really good? He put me under a lot of pressure with his overpair; did he think he was good (and value betting), or was he turning his hand into a bluff? Is this the type of play I can expect (i.e. repping strength on a 3 heart board?) This particular table seemed especially difficult; the most difficult that I've played at so far.

Fortunately, I got good hands, which held up - as evidenced below, again:

This is from 30th hand so no real reads, same table, different player...
Full Tilt Poker $0.25/$0.50 No Limit Hold'em - 9 players - http://www.thehandconverter.com/hands/263052
The Official DeucesCracked.com Hand History Converter

CO: $15.10
BTN: $58.15
SB: $34.50
BB: $38.70
UTG: $59.35
UTG+1: $52.75
UTG+2: $9.75
MP1: $29.25
Hero (MP2): $107.95

Pre Flop: ($0.75) Hero is MP2 with 9d Td
2 folds, UTG+2 calls $0.50, 1 fold, Hero calls $0.50, 1 fold, BTN calls $0.50, 1 fold, BB checks
Nice suited connector limp from MP. I'm limp / planning on calling a PF raise.

Flop: ($2.25) 2d 9s Tc (4 players)
BB checks, UTG+2 checks, Hero bets $1, BTN calls $1, BB folds, UTG+2 folds
Fairly dry board, QJ & 78 play well here, so I lead to deny odds and hopefully get a call from a lesser hand (AT, KT, QT, etc.)

Turn: ($4.25) 5c (2 players)
Hero bets $3, BTN raises to $9, Hero calls $6
He's playing a small pot with a flat on the flop. Now the 5c hits and he's blowing up the pot? What did the 5c change? It puts 2 clubs out there as well as the T9 straight draw, but is that enough to make BTN want to play a large pot? The only two hands I can put him on are: Overpairs (limped BTN AA-TT) or 22 for the set. However, thus far, his line does not make sense.

River: ($22.25) 5s (2 players)
Hero checks, BTN bets $18, Hero calls $18
That's a HUGE bet, and unfortunately, the second 5 pairs the board, making all overpairs better than my top two. This is a HUGE aggressive play, making a pot bet on the river after raising the turn. His bet sizing is a little out of whack for an overpair or any made hand. If he's truly value betting me, I would think a $10 or $12 bet would be more appropriate. Perhaps my flatting the turn gave the impression of weakness, but I was certainly surprised with the turn raise. I have shown weakness by checking the river, figuring that betting out is only going to lead to getting called by better hands at this point. I have to believe that my opponent thinks the same thing, and therefore bets out, big enough to try to buy the pot... This is one of the few times that I am going to make this call - and I consider this to be a "hero" call.

Final Pot: $58.25
BTN shows Qc Js (a pair of Fives)
Hero shows 9d Td (two pair, Tens and Nines)
Hero wins $55.35
(Rake: $2.90)

Overall, is this the kind of play I can expect at the $50NL level? I am not getting any of this level of aggression at $25NL, and I'll tell you, if I had AT on the hand above, I probably would have folded the turn, which would have been a mistake. Is this donkishness or clever play?