UTG A9o, then a few questions

[inanevoyage]

PokerStars 2/4 Hold'em (5 handed) converter

Preflop: Hero is UTG with 9[img]/images/graemlins/heart.gif[/img], A[img]/images/graemlins/diamond.gif[/img].
<font color="#CC3333">Hero raises</font>, MP calls, <font color="#666666">1 fold</font>, SB calls, BB calls.

Flop: (8 SB) J[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, BB checks, <font color="#CC3333">Hero bets</font>, MP calls, SB calls, BB calls.

Turn: (6 BB) 4[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, BB checks, Hero checks, MP checks.

River: (6 BB) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, BB checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP raises</font>, SB calls, BB folds, Hero calls.

Final Pot: 12 BB

First off, i'm wondering whether or not it is better to raise this when im UTG looking for a flop? I've done both, but i've never clearly read what way is +ev in what situation. Play at this table was extremely loose, and this move(which i wouldn't have done a week ago) seemed right.

My second question comes on the river play. Considering the preflop raise, i felt either one of them could have a higher two pair with AJ, but is calling the right answer here?

Any input appreciated, thank you.