As a professional web designer already "in the game," I would encourage you to do anything you truly want to do. That's how I got to where I am today. There were plenty of web designers who considered themselves "pro" in their minds that were merely script kiddies when it came to HTML and Javascript.
Give it a shot. From my understanding of where you're at now, you won't be developing and selling CMS themes for weeks or months. I am being very realistic and honest in my estimation.
The professional web design industry is very competitive... don't let anyone try to dissuade or discourage you from possibly butting into their market and taking their clients. You'll find many of those amateur types lurking around forums finding any potential competition that may come their way and try to snuff them out in the name of principles, education, insecure elitism or whatever. Screw'em. Odds are, your ideas are ten times better than theirs because they come from within, instead of manifesting themselves out of the urgency and immediate obligation to pay off student loans.
Sure, we web designers hate losing a bid to a college kid that'll do it for 90% less than us, but in my opinion, web designers that rely on clueless, naive, and otherwise ignorant clients that will pay next to nothing (see: getafreelancer) per project should know what's coming before they even send their first bid: futility.
Don't bite off more than you can chew. Create a simple website for yourself, like I said a few posts up. Then look for a client you're comfortable with that knows your intentions, motivations, and limits, then begin.
Good luck.
