Actually, It is expensive, but a bit cheaper than many other widely used DAWs, like Abelton for example.
You can get the Producer Edition for around $200 and the full (Signature) Edition for around $299. It comes with some good vsts and such so I'd say it's worth it. IMO, I like it better than Abelton Live. I recommend buying it, It's not about the virus issue or legal issue or anything, but it's about how you progress, Knowing you spent money that you earned by working hard on a tool rather than getting it for free can improve your production and level of investment on the program, and thus, you can learn it better.
1) If you ever get a new computer, go download a demo for FL, and once you make enough money, upgrade it to the full version, However, there's a free alternative, It's called REAPER, it's CPU light and Free! and if you want to publish your music or sell it, you can get the licence for it, which is only $60, Trust me, I used both of these softwares.
FL Studio : http://www.image-line.com/documents/flstudio.html
Reaper : http://www.reaper.fm/
2) Try searching up theory tutorials on youtube, There are TONS out there.
3) Gradge band is a fun program to use, though it's a bit limited in some parts reliable for audio production, if it's the time, you can upgrade to logic, which is more suitable if you decide music is your profession.