Personal Accounts on Vercel are great for hobby projects. Once you need to deploy more powerful sites, collaborate with other people and customize your workflow, Teams are the right way to go.
Migrating from a Personal Account to a Team previously wasn't possible without incurring downtime. It required removing Projects from their old location and deploying them again in the new one. As of today, it's only a matter of a few clicks on the dashboard.
Transferring projects without downtime is now as easy as navigating to the Advanced page in the Project Settings, following the flow and watching the magic happen.
All Deployments, Domains, Environment Variables, and any other configuration of your Project will automatically be moved to the target Team for you. Even optional features you might've enabled can be transferred over.
Check out the documentation as well.