I've been developing websites since I was fourteen, now 25. It has been my full-time job since getting into the "real world." Opening a business like this can be easy and difficult. First, all you really need is a website and word of mouth to get it going. That's pretty cheap - pay for a domain+hosting, do a little homework and get your website up and running. Build one website, do a good job and word of mouth will bring in more.
A problem that you will experience is your competition. It's not likely to be the competition down the road that runs a business similar to you...it's the template design companies. I can't tell you how many times you'll get "well i can go online and get something for $100, why should I pay $8000 for your service?" This will be your main roadblock. You need to be able to differentiate yourself from those template companies. 9/10 you'll get turned down because of this reason, but don't let that get in your head. Just keep chugging along.
Best of luck and let me know if you have any specific questions.
Michael Terry | SquareType
info@squaretype.com
www.squaretype.com