If you have “many clients and many projects” you’ll almost certainly need to use the 3-digit projects.
I’d keep one ‘project’ for your personal life. It should easily fit within one, try to keep it simple.
For the freelance stuff, try to develop a structure that you can just copy/paste when you get a new client/project. I’d guess that each client would get its own project number but this will depend on the nature of your work.
I need to develop/publish some templates for this sort of thing. Am interested in what you come up with if you can share it?
I do wonder whether it would be useful to keep your clients sorted alphabetically while still assigning them a number, a bit like how I explain in this post?