If I continuation bet on flop should I just give up the pot then or 3 barrel air my stack away?

Ha I'd answer all your questions, but I'd have to write a book. In general though, if your opponent has a high fold to cbet% (over 60%) then you wouldn't want to db hands worse than top pair 2nd kicker or combo draws. If his fold to cbet% is very low (under 40%) you are going to be able to get him to fold more frequently by firing the 2nd or 3rd barrel so you can bluff him more often. Be careful though, because some of the people with low fold to cbet%'s will also have low fold to turn and river cbet%'s. Don't try to bluff those guys. Just go for thinner value bets because they will call you down with 3rd pair.

At low stakes games, the only time you really want to be 3 barreling with air is when you are almost sure the guy is on a missed draw and you don't have much showdown value. You could also 3 barrel bluff scare cards. For instance, if you are against a guy who is 60/30 vpip/pfr, and the board is 3hQh7s, when you see him snap call your cbet and the turn comes 2c and then he snap calls your db, then the river comes 9c you might want to bet again with your whole range because there's a very good chance he had a heart draw. The opposite is also true against better players. If the board is 3hQh7s and your cbet gets called by a tight guy, he likely has a pair. That means that if the board runs out with running hearts you might be able to 3barrel him and represent a flush.

A lot of it depends on how your opponent sees you and how likely he thinks you are to bluff. I wouldn't get in the habit of 3 barrel bluffing people until you get to at least 100NL (and probably not even much then). The spots that it will work at low stakes games are so rare that you end up costing yourself more money than you gain from your successes. It's something that you can do from time to time but you need the perfect board and the right opponent.

In general you want to double barrel scare cards and cards that give you additional equity like backdoor draws, then you bet rivers that are scary to his range and ones that improve your equity further.