1. Yeah I assume most villains will be 4 betting AK, AA KK here. I'd expect AK to be a 4-bet from a std 100NL reg almost alwyas without some dynamic or reads that I'm a nit. AA/KK may sometimes flat thinknig that they often just fold out a ton of my range by 4 betting, but I think this is much less likely than them 4 betting.

2. On the flop we get to take down the pot enough for our c bet to be +EV. The flop obviously makes his AJs and AQ combos unlikely yo be foldoing at any point. Our c bet on the flop has the immediate implication of being able to fold out some hands that he doesn't choose to float with, like his lowest pps or some hands with little equity like KQ (which me are ahead of, but this doesn't mean we shouldn't try to make him fold them because c/c against his range as a whole is likely going to be bad and these hands have decent equity vs our measely pair anyways.) So even though the c-bet is good because directly it only requires him to fold just over a 3rd of the time, it's also good because it sets up what I consider to be a +EV turn bet too, by folding out the range I listed in my examples - the 51% of his continuing range that isn't Ax or better. It's better to think about what hands will continue on the flop instead of what hands "hit" the flop when making a c bet.

3. Yeah this could be helpful if you had a shitload of hands and a sample from 3 bet pots where ranges and therefore tendencies are usually different. Usually though, we wont have this good a sample or reliable a stat, so we need to be making a likely range for him and thinknig about how he's likely to play it. Our read of his range and how he plays it wont be perfect because our information is imperfect, but we can get pretty close usually by making good assumptions and educated guesses.