1. Bet every time, if there are three of the suite and you are reraised consider folding according to reads
2. Reraise every time, pay of the AA in the rare occasion it does happen, more often then not you will find yourself vs AK, QQ or worse
3. Sure, in tons of situations, the first that comes to mind is continuation bets and draws when there are multiple players i the pot. As the table gets shotrhanded betting with middle or even low pair sometimes makes sense (in HU I usually bet every pair)
4. If you are not willing to bet the A9 when A comes on the board why play the hand in the first place ? Hoping to catch two pair ? Fold preflop and save yourself a world of pain