The prototyping functionality is awesome! Imported projects do not get the same level of treatment from Gemini however. The ability to merge projects seems to be somewhat hampered as well. I have a Software Engineering background but my level of coding expertise is not enough to be able to do much more than design with the current functionality.
I suppose the worst thing is the ability of Gemeni is not agentic in the ide for imported projects and it requires me to manually cut and paste pieces of code. Here’s to hoping for more powerful support for existing projects in the future. 
You can start a prototyper project and then unzip your existing project into it, erase the context of the prototyper and then have it start fresh with your imported project.