The 10,000 hrs of practice thing is kind of interesting.
Back in 2009, I got sick of corporate publishing, a contract job I picked up after having done small press publishing for years, and decided to go with passion instead of money by becoming a bicycle mechanic.
It took a couple years before I was at all comfortable checking in a bike, finding the faults which needed to be repaired, and was confident that I could fix them. Every day, there was still something new in the workstand I'd not seen before. But little by little confidence and skill accumulated to the point that I'm now fairly confident about being able to effect nearly any kind of bicycle repair, build, or modification.
Just did the math: 40hrs/week x 52weeks/yr x 5yrs = 10,400 hrs. Heh.
Thing is, I still don't feel anything like a master mechanic. If anything, journeyman.
------------------------------------
If you want to be a writer, start writing. Write every day. Doesn't have to be good, in fact a lot of what you first write won't be, but without practice it won't get good.
From a publishing POV, write in MS Word, or a program which can export a Word doc. If you have art, it needs to be 72dpi for online/ebook quality, 300dpi for print quality.
Self-publishing is fine, but remember that it also requires self-promotion to become successful at it. In fact, even if you are published by a publishing company, don't think you can rest on your laurels, you will still need to relentlessly self-promote.
Outside bestselling authors, most authors do not make a living writing books until they have many, many books in print.
Oh, and one of the total guilty pleasure books I love to read is The Destroyer action/adventure/humor series. Co-author Warren Murphy has been at it for decades, and has had published over 200 books. On his website he has posted a "Writer's Class" series of instructive articles:
http://warrenmurphy.com/writing-class/