If you learn on Reason, it makes you a hell of a lot more knowledgeable in general, because of how it's set up. FruityLoops is set up so a chimp could use it, not so you actually learn something about mixing. Whether that's good or bad ultimately depends on your mix, in the end.
I always recommend starting on Reason, even if you don't decide to stick with it (I use Live), you'll have a really solid understanding of the fundamentals of music production, and it'll be easy to pick up any other software on the planet. FL also teaches horrendous sequencing/mixing/production habits, and actually makes it harder to switch off of it into more "standardized" software, like Logic, Pro Tools, Live, Sonar, Cubase, etc.
I'm also going to say that there's not some magic number which at that point you suddenly become good at mixing, but it'll probably take you at least a year or so before your stuff becomes reasonably good, at least mix-wise. Everything you mix early on sucks, I don't care what you think of it, it's a fact of life, and everybody else's does too. As you keep working on it, you'll end up learning what works and what doesn't, and (hopefully), your mixes will be more and more solid.