You can make a “decent” living as a supplement to your “day job”. Now this is actually a chicken-and-egg situation.
In order to become a fully employed on-demand voice talent, you’ll need to go full steam ahead. Save up 6 months of savings, quit your job, and get the hell out and start networking and building your network. Start creating new voice demos (commercial and narration demos are a great place to start).
 
Setup a home studio and LEARN how to use it properly. If you go to our voice talent page, you can hear your competition. You need to be AS GOOD, but preferable better, than anyone on this page. These are the folks who are making a decent living at their craft. They’re going all-in and dedicating their full time to self-promotion and self-improvement.
 
If you’re don’t have the courage to quit your day job, then you can get by doing this part time. But don’t expect to be taken too seriously from the people who really have the money to spend on good talent.
This is all just my opinion from experience. 😀