Ring game player poppin his cherry questions (low quality)

[Alex/Mugaaz]

1. When you're playing 4-6 handed and are in the BB, what unpaired hands are worth 3 betting against a non-steal raise? I usually have been 3betting any hand I feel has equity against his range, but I feel that some of my 3bets are incorrect becuase the equity advantage is too little compared to positional disadvantage (obviously this is soemthing I should of figured out in ring game play too, but it happened much less). Is there any formula to calculate what range you should 3 bet vs his range of openers?

2. When you open raise and only get called by the BB, SB, and/or both;

Under what conditions would you check behind on the flop holding overcards that include an ace?
Under what conditions would you bet the flop and check the turn?
Under what conditions would you lead both for the free showdown?

3. This is a question I feel stupid before even asking. Should you/how often check behind on the turn and/or river against a tight caller who is also super passive and will c/c even with TPGK or 2p?