Re Portfolio for each client: That’s one of a number of possibilities but I can’t say that’s the best option necessarily. It would force you 1) to have a project for each endeavor for each client and it’s not clear that’s needed, and 2) it requires Asana Business which you might otherwise not need.
Another alternative I often use is what I hint at here, but again this is something I reserve for clients because the right approach for each can only be determined with some discovery first: