1. You're paying 1bb every big blind. If you fold, you are losing that 1 bb. So if you fold 100% of BB, your winrate in the BB will be -100bb/100. This means that any hand that performs better than -100bb/100 should be called instead of folded, because it performs better than folding.

Similarly folding in the SB 100% will yield a winrate of -50bb/100. So any hand that performs better than that should be played.

Similarly, if you fold from UTG-BTN 100% of hands your winrate in these positions will be 0bb/100. So you should only play hands that perform >0bb/100, which makes sense. Only playing hands that will be profitable. (though it's possible you may sometimes play -EV hands in isolation, if your overall range benefits in EV from playing that hand).

2. Yah you really need to find spots where one pair could be good. Again, you only need to be good 30% of the time to make a profitable call! You can lose 7 out of 10 times often, and it's STILL the correct call.

3. What is your steal sizing? yah just checking your steal success %. Given you're tight, I'd imagine it should be high.