If you made the cake in your avatar photo, you probably don't need the Wilton classes.
I am a huge advocate of attending the classes (that's how I began with zero skills), but they are definitely for beginners, not medium to advanced cake decorators.
You would be better served to seek out a Cake Club in your geographic area. The best place to research the location would be to contact the nearest specialty cake supply store or look through the ICES website:
Cake Clubs and/or ICES sponsored classes will offer the higher level of instruction that help you advance in the craft.
Here is a link to a thread I created after two years of cake decorating classes and conventions and hundreds of hours online. The information will go from the very basic (first time making a level cake), to links for medium to advanced techniques.
On the other hand, if you are considering starting a side business, you WILL need to prepare a business plan and do research on pricing, contracts, etc.
CakeBoss offers superb software and the internet will have a lot of sites regarding how to prepare a business plan. (CakeBoss offers a discount to CC forum members.)