I cant give you a % but consider this. Before I considered quitting my full time job and playing this is what i calculated daily in my head before I mad the plunge.
Even if you have been having a good long winning run at the 10-20 level (say, six months of regular play), that's not necessarily enough time to judge yourself. It's probably more realistic to hope that you can make one big bet an hour, and a $20 an hour job, with no benefits (health insurance, paid vacation, retirement, etc.) isn't such a terrific job. Figuring a 40 hour week, that's 40k gross a year, before all the taxes and living expenses. That doesn't leave much room to handle unexpected expenses or savings in that budget. Most players who play for a living need to play at higher limits, and the opposition at higher limits is tougher
This is actually quoted from somewhere, but i had copied it to my harddrive a long time ago and use to use this. Now I realize you probbaly dont care about going pro but im just giving you the idea that i based my playing on so take it for what its worth.
As far as books, the best book for me was super system. Super system 2 is out and I hear its real good but havent read it yet. Also anything by David sklansky is gold too learn but its mind boringly dull and very hard to get through.
The best resource for me however would actually be poker forums such as 2+2 because you can actually go there and post hand histories and ask others advice. However you have to be careful because some people are idiots and will give you ****ty advice. Really the best way to learn is just to read and to play for a few years and lose lots of money.