I started my homelab with a small form factor PC (not a NUC specifically, but similar). They can be very capable servers, depending on specs and your needs.
As for towers, you can do standard consumer workstations, too. I game on PC, so when I build a new rig every 3 or 4 years, my old one goes in the closet. Sometimes I just add it and have another server, sometimes I donate the current server to a friend or school. Point being, you don’t have to have a Threadripper CPU and ECC RAM to run a server.
That being said, if you plan on hosting critical services or non-critical-but-public services that you want to have high availability and stability, it might be a good idea to upgrade to enterprise hardware eventually. But definitely not needed if you’re just starting out or running personal, non-critical stuff.