First thing is to be aware that it should take minimum 6 months to become semi pro, with intense learning.
Fiding material is easy, but stick with theory, and mental, there are plenty of ways to play poker and still be winning, you'll have to discover your own way.
Bankroll is key to do not lay down. You should deposit one time, a one time redeposit is ok, but no more. If you do, you messed up somewhere.
Don't withdraw, all winnings should go to your bankroll, unless you feel that you won't be able to psychologically get the stake up, than put a minimum limit (for exemple, you reached nl25 with a br of 1000$, but you don't feel confortable playing nl50, then, put a limit of 1500 for exemple and when you reach 2500$ you can withdraw up to 1000$, at this point you can call yourselve semi pro, untill you feel confortable to climb to nl50).
You don't have to spend money on learning, specially at the beginning, you can read books, but don't follow them as if it's the way of achievment. Find people with whom you can discuss your plays, and if you don't and have money to spend, take a coach, but a good one. Read articles, work the maths, don't be lazy, it's not calculus, just division and multiplication, and some addition. You have to feel confortable with your decisions, if not, write it down, and review it later, winning or losing.
If you want to become pro for the money, it will take longer, because you will have to lose some, and it's painfull.