1)yup
2) yup
3) you factor in scare cards as "bluff outs" into your pot odds equation (e.g you have a flush draw on a K high board and you read your opp as having 1pr ks or worse with q or worse kicker, you can factor in that you'll be able to bluff an A turn a fair portion of the time (say 75 %), you can add 75% of said As into your pot odds equation (3/4). so with a flush draw you have 12 outs- 9 to hit flush and 4 to hit an A turn where you can successfully win the pot with a bet 3/4 times.
4) kind of, but obviously we need to calculate HOW MUCH + or - EV it would be.