1) sample size needed = as many hours as you can play. You should be playing every Saturday and Sunday as well as any nights you have free. I wouldn't start the new year without a solid summer of play under my belt to know where I stand before classes start.
2) Take notes while you play. If you do this there won't be any downtime. You will either be taking notes on your last hand for analysis later or taking notes on how your opponents are currently playing. There is a lot going on at the table so watch it all.
As for fatigue, get up and take a walk around the casino. You don't have to play every hand.
As for stacking off, that's a mental hurdle. Its a lifelong game. Does it matter if you stack off at the end of this session or the start of the next one? No. Sounds like you lack confidence a little bit.
3) 1/2 live is much easier than online.
Quote:
I feels like nothing I learn from studying or the edge I'm building ever takes shape because of who I play against.
You're at $22/hr so far. If you maintain, that is a solid win rate, but beatable. You should be asking yourself why you aren't winning $30/hr and plug the leaks. So, you still have things to learn, at least about beating players at 1/2 for more money. If it bothers you that much, jump up to 2/5 or 5/10.