How To Play Pocket Pairs Game

There's no simple optimal formula for playing small pocket pairs. If there were, everyone would play them the same way. One major reason is that the factors that can impact your choice of action depend on more than just the cards. As a fairly simple example, if you miss the flop, it's much better to bet into someone who plays weak tight and thus will often fold hands like a couple of overcards or pairs below top pair than into someone else who will call or even raise with those same hands.
 think these cards are worth a limp and sometimes a raise, especially if the table is weak/tight giving you fold equity or you have good position. Frankly, playing ATC on the button at a weak table can be profitable if you're willing to bet the pot on an unraised flop, and a pocket pair is better than ATC. The odds of flopping a set or better are 7.5:1, and if you do hit the flop, there's a good chance you'll win better than an 8:1 return on your initial call. If the table makes a post-flop call cheap, the odds of hitting a set or better by the river are 4.2:1 (from pre-flop, not post-). These hidden sets are some of the most profitable hands in poker, especially if opponent plays top pair or two pair strong. Yes, you'll lose most hands with small pocket pairs, but it's not about winning hands, it's about winning money. Sometimes you get beat set over set, but not too often.
I'll limp with a small pocket pair any time I can, raise in late position and call some raises in later positions if the conditions are right.
If several limpers, you can play your small PP as a drawing hand like suited connectors. That's really what it is, unless you play it aggressively, in which case you're trying to establish an image and are willing to consider CBs on a missed flop. The limp is probably safer and potentially more profitable. Bigger pairs deserve more protection.
On the other hand, especially if you're playing against skilled and observant opposition, you want to disguise your hands by playing them more consistently, regardless of holes. You don't want your bets to telegraph "small pair" or "big pair" because you always play one one way and the other another way. Against more skilled opponents, you'll have fewer limping opportunities anyway. Then, it's either raise or fold. Ans since more pots are raised, you'll probably be folding more of those small pocket pairs. And if you're in early position, you're either going to want to fold or make a standard raise - not a mini-raise.
If you like limping, look for tables with a big percentage of players seeing the flop. If you're not yet a very good player (be honest), avoid those tougher tables.
I love low pocket pairs in the right position with the right implied odds, so you have to consider stack size. If it costs more than about 12% of your stack to see the flop, you're not getting the right risk/reward ratio. Factoring in the times you hit your set, but don't get paid off (why do those flushes always hit when I have a set?) If you don't have at least 8 pre-flop raise, lay em down.
Most of the time the correct answer to such a general question is going to be it depends on the type of game, type of players, your image, your relative stack size, etc. But your post does bring up one area that I am keenly interested in. What do you do when you hit your set? The first decision is will you bet or check your set? I have tried both and here is what I've found. If there was little pre-flop action (limpers or small raises), then betting usually results in your opponents folding. If there was some pre-flop action (standard raises) and big card have come on the flop, then I have found a bet is more likely to be called or re-raised. Another aspect I take into account in decidng whether to bet or check on the flop is the texture of the flop. For instance have three cards of the same suit hit the board or three connected cards hit the board. I will usually bet half to 3/4 of the pot on these boards to gather information. If I get any callers, then I usually slow down and may fold if my hand doesn't improve. If I get re-raised, then I make my decision based on whether I read my opponent to be the type of player to raise like this with a draw or will raise like this with a made hand trying to appear to be on the draw. I'm just scratching the surface of one of your points but my response is getting pretty long.