Regards. The doubt here is not about how to create the website, it's the business side. The marketplace I want to create is about web templates, And without any web template and without web designers, how can I make it grow? From scratch to huge? Any tips, any experience: please tell me.
Populate it with templates from as many different web designers as possible, and then seriously advertise it. If you coded a custom marketplace even better, you have something unique. If not, no big deal, but you still need to advertise! It must be user-friendly, so both the theme creators and buyers can buy/sell their themes without any complications. It must be EASY to use, because if your website is new all it takes is one frustrating step in a form and the user might decide to go somewhere else to buy or sell a theme. First step.. get your website up so we can see it!!! What are you waiting for? Please explain where you're at now and what's holding you back from taking the next step. This is not going to be easy, but I have a feeling you know that. Let's see how serious you are, because I am very interested in seeing your marketplace!