Lets call in some HUD professionals:

The legendary @w34z3l
The one and only @eroticjesus

These guys will help you a ton!

Also @Komododragonjesus will have a few words of wisdom!

Check out this article maybe.

here is a screenshot of a few of my popups. They are actually a bit more advanced now even, so screenshot is about a year old, but should give you a rough idea of what to do with them. As a rough guide, every stat on your HUD should have a popup.

Having the right stats up can definitely help your game. What I did for most of my poker career was basically to take anything that I frequently looked up in popups or in PT4 between sessions and make it easily accessible on a HUD. It's a pretty simple approach but it's worked for me.

Off the top of my head, won when saw flop (WWSF) and went to showdown (WTSD) are good stats if you don't have them. Combined they give a good impression of a villain's overall strategy. For example, if they're winning more than their fair share when they see the flop and their went to showdown is low you can get the impression that they'll be bluffing quite often compared to players with different stats. You can use with with won money at showdown (WSD) as well to estimate how value heavy a player might be.

As for session length, that's unique to everyone. There are players who can play 12+ hour sessions and players who can only play 1 hour. You seem to have a good grasp of where your limit is so stick with that and take breaks when it gets too long.