It depends on your hardware. If you ever get a new CPU with eco cores, then you'll need 11, or you will have performance issues.
As for running 10 without security updates, I doubt anyone will notice the difference. If there's a serious issue, they will likely give everyone updates. They're still doing virus updates, so the only thing most people will notice is fewer times to restart their PC.
If you really want updates that much, you can install Windows 10 IoT LTSC over the top of your existing install, keep your files, and get an extra few years of updates.