Your question is slightly all over the place but I'll try to answer it the best I can.
First, it seems like you've fallen prey to a common mindset issue many, mostly recreational, poker players have. You shouldn't be measuring your results by what you're currently up or down during one session. You'd be surprised to learn that winning players are really only going to have winning cash sessions something like ~55% of the time over the long run. As such, you shouldn't be focusing on the current results of your session, you should be focusing on the quality of your play, your current mindset, how tilted you are, and so on.
Cash players measure their results in something called big bets per 100 hands or BB/100. A big bet is simply two times the big blind. So in $0.01/$0.02 micro-stakes cash, a big bet is $0.04. So when a player says they are an 8BB/100 winner at $0.01/$0.02, you know that, on average, for every 100 hands (normally about an hour worth of play) they put in at a $0.01/$0.02 table, they will make $0.32.
Note that isn't that much. And that's what winning players are making. If you're a slightly profitable, or breakeven player, then over the long run you'll make much less per hour. So when you're sitting at a $0.01/$0.02 table, you shouldn't be worrying about what you're currently up or down. That piece of information is completely irrelevant. It doesn't help you play better poker. For most people, it will usually tend to put them on tilt. For instance:
- I'm up three buy-ins, I need to quit now while I'm ahead. You stay for another hand, lose your whole stack, and go on life tilt because you "knew" you should have left.
- Your down two buy-ins but, despite not being tilted or in a bad mental state, you decide to quit for no reason other than the cards aren't going your way.
And so on. The point here is that one of the most significant things you can do for yourself as a poker player will be to stop focusing on short-term results. Poker is a game where the profit shows up in the long run.
So when you sit down for a cash session, know before you start how long you want to play for. Set concrete time limits. For instance, I strictly play 60 minute sessions of heads-up hyper-turbos on PokerStars. No more, no less. Then I take a break, evaluate my hands, and do another session if I'm feeling up to it.
And then be honest with yourself during your play. If you know you get tilted if you lose 2-3 buy-ins, set a stoploss. For instance, lots of cash players will quit the game entirely for the day if they're down three buy-ins, simply because they know they won't be able to play their best. And even if you aren't down three buy-ins, but you know you are tilted, or tired, or just playing badly, leave. Quit.
The idea is to put in quality volume. Leaving a cash table when you are playing your best and are in the zone simply because you've won money is a bad, bad idea. You need to capitalize on when you're playing your best. Don't say you'll leave after you gain/lose this much, say I'm going to play 60 minutes of $0.01/$0.02 and try to make the best possible decisions I can, regardless of the outcomes.
1) Are NL2 micros for building your bankroll to move on higher stakes rather for money winning purpose ?
Honestly, all micro-stakes games aren't going to give you a good hourly rate, even if you're in the top 1% of players. Micro-stakes games are for building a bankroll while you're learning how to play.
Consider this. Every single person that decides to play poker will have to pay $$$ for their poker education. Lots of new players will be losing players for some time before they become skilled enough to win consistently. So at what stakes do you want to pay for your poker education? Micro-stakes $0.01/$0.02 or mid-stakes $2/$5? Obviously micro-stakes. Just keep in mind that the focus when you're playing micro-stakes should be on learning and improving instead of grinding out volume. Review your hand histories, watch videos, and so on. This will pay off so much in the long run and when you move up you'll be well prepared to crush.
2) What do you consider enough for a starter trying to practice his book theory ? playing tons of hands per-day or winning that much or get out when you bored / tired / distracted etc. ?
Put in as much quality volume and quality study/review as you can per day. If you know you're tilted/tired, stop playing and study/review. Do NOT fall prey to the tendency all new poker players have to become an autopiloting grinder at micro-stakes. This is basically poker purgatory. It's far more important to play, say, 2-4 tables of cash while focusing on making good reads and decisions instead of mindlessly grinding 16 tables. So, so many people, myself included, have made this mistake.
Also consider buying Jared Tendler's Mental Game of Poker. It's considered the best book on managing poker tilt out there.