Hey TheMuMyung!
I play Midstakes MTTs for living.
Best advice I can give you:
1) Set clear goals. (I could talk hour about this, but I just recommend you to watch videos about the subject.)
2) Get some private coaching. (you don't have to reinvent the wheel.)
3) Get close to right people. (Nothing is more important than having friends with same goals and interests.)
4) Join into studygroup. (If you can. There's a lot of value in this. Not just reviewing hands, but that you're actually a group that works together. You will congratulate each other for success and support each other when in a downswing.)
5) Don't just study poker.
(You should focus to improve as person and as entrepreneur. Even tho you would have Phil Iveys skillset, it doesn't guarantee success.
You need to learn how to not tilt. You need to learn how to work hard, but also how to work smart. You have to learn how to handle stress and live a happy life, because poker can be very depressing some times. Money isn't worth it if you're not happy. There's lot of stuff that can be useful, but you don't find it in the pokerforums or strategyvideos. Be creative and use your imagination and you see the full picture.)
6) Grind, grind, grind!
(Success in MTTs comes from the grind. Even tho the studying is really import, MTT is very simple. You will learn most of the stuff just by making same mistakes over and over again and analyzing afterwards. That's why you should just play a lot and get privatecoaching every now and then instead of reading 1000 poker books and spending 1000 hours in livecoachings. You will learn the most by doing the mistakes yourself.)
- Which movies on PS.com can be the most usefull in the beggining?
- Which site should be my battlefield? (I heard about 888 but I am not convinced to their soft and PS is too high i think?, iPoker? FTP?)
- Should I first learn about all of the starting/pushing ranges?
- How can I improving my game?
- I can't recommend you any videos, it's been too long since I've watched any. 
- I have money in 12 sites and in each session I use at least 8 of them. Really depends on the day. If you play small stakes I recommend you to avoid pokerstars and play small field tournaments (less than 300 players) buy-ins lower than 22$ freezeout, 11d rebuy. Very easy way to build a bankroll no need to play 180mans or any other SNG forms. You will probably need at least 1k$ to start tho. In long term you want to add big field tournaments like big, hot tournaments in pokerstars, but you need a lot of bankroll. When you have 1000 ABIs you can play pretty much anything you want.
- This is good push fold chart for regular tournaments. (in turbos you need to adjust a little bit) http://www.pushfoldcharts.com/fullring/
- I think I gave you multiple ways in this post for how to improve your game.
Hope this helped, good luck at tables.