Welcome to Geekhack!
Seems like csmertx has already provided you with a wealth of links and information
The thing to do is to start now. If you keep researching, you'll reach the point of information overload, but still have no practical experience.
Once you have enough info to start, by all means start. Practice makes all the difference here. Try a few designs and processes - you'll probably make a mess the first few times. Almost no-one comes out with perfect keycaps on the first try. Or second. Or third. It is an iterative process that is best, well, iterated until you find a process and materials what work well for you.
Good luck