Thank you for your questions!
Pricing and business models are complex indeed, and require a lot of thought, which becomes easier when you have started and been running your business for a while. I think the best way to get started is to define one service that you know you want to offer, and set a fixed price for that. This could be a Design Concept Creation, for example per room pricing, and then use per hour pricing to run your first projects beyond that fixed price.
Once you have an understanding of the time spent on different projects, I’d move to a combination of fixed price + commission + percentage.