In the article “Is becoming a WordPress Professional right for you (or even possible)” written by Tom Ewer, he mentions a few pointers for people who want to do WordPress as a profession. While doing so, Tom tells of 4 WordPress users who had little to no knowledge of WordPress become great theme and plug-in developers. WordPress has helped these users find their niche in the WordPress community.
Becoming a WordPress guru is an endless learning curve. But then, the same can be said about a great number of professions these days. If you have transferable skills, then you already have an advantage.
He also says:
Most people who ended up making a living with WordPress didn’t set out that way, but came from other design, coding, or creative jobs. With the phenomenal growth of WordPress, they simply found a lucrative niche and became the experts in it.
If you are wondering about doing WordPress as a profession, Tom Ewer mentions a few pointers and gives some examples of users who became great theme and plugin developers in his article “Is becoming a WordPress Professional right for you (or even possible).” If not, still give it a read. There might be something there that could help you with a profession in web design and development.