How did you learn to make your own miniatures?

I just finished my first diy rolife kit (Sam's Study). I really enjoyed it! But also, I missed the design/creativity aspect (I make art as a hobby).

I feel like I would like to start designing and making my own miniatures and rooms. What are good resources for learning? Where do I find materials? Should I learn some carpentry and upholstery (to make furniture components)? What tips do you have? Is this necessarily an expensive hobby? What do you wish you knew, starting out?