1a) High PPs are very strong hands but their equity drops dramatically on the flop and often more so on the turn. We want to get as many chips in the pot as possible at the point when our equity is highest to maximize our EV. With large PPs this means building as large of a pot as possible preflop.

1b) When we have a big pair preflop, we want to start working to reduce the implied odds we are offering our opponent to see the flop and turn and pull ahead. Raising and 3betting PF reduces the implied odds our opponent gets to try and do this with hands like lower PPs and suited connectors.

1c) Since bet sizing is normally based on pot size in NLHE, we need to take advantage of opportunities preflop to increase the size of the pot so that we can bet more chips on later streets so we can win as much as possible. The most efficient way to build a pot over the course of a hand is with moderate sized bets on each street.

2) When we are defending against 3-bets we want to 4-bet our hands that are sufficiently ahead of what Villain would 3-bet, enough bluffs to balance the number of hands we 4-bet for value, and call enough of the rest of our hands to make sure we hit our minimum defense frequency. That calling range is made up of the strongest hands that are too weak to 4-bet for value. Most pocket pairs fall into this category based on that alone. This is enhanced by the fact that they can flop sets and depending on the size of the 3-bet we can sometimes call even hands like 22 just to try and flop a set.

3) I don't understand what you are asking.

4) Since the rake at uNL/SSNL is pretty heavy, it is perfectly OK to fold hands that would would be break-even before the rake is accounted for.

A lot of these types of questions could be solved by investing in a set of GTO solved preflop charts. There are a number available out there for purchase. While it may seem a bit expensive at first look it helps a lot to have a solid GTO reference to start from that you will need to start building exploitative play, saves you the trouble of trying to create good ranges yourself, and saves you the money that would be lost from building them wrong.

sjfraley1975 summed it up very well

To answer question #3, it doesn't matter if you are 400bb deep if everyone else is 100bb deep. Concentrate on the effective stack sizes (ex. you have 350bb and opponent has 250bb, effective stacks are 250bb). If you are uncomfortable being deep (many many players are) feel free to exit the table, bank the win and buy back in. Not sure if there is wait time to get back on a table on the site you play. On Ignition/Bovada, you can come and go as you please, even if you only miss one hand.

Stop limping altogether.

Just always raise KK+ at the microstakes. You really don't have to get that fancy.

You trap with the nuts when you think the value of trapping is greater than the value of raising. Maybe they bet a lot against your flatting range, but overfold to your raising range. The other side of that reasoning is that trapping helps defends the rest of your flatting range to prevent being run over.