NUCs make really nice homelab servers. They can give you a lot of power while not sucking too much electricity. I have used three NUCs to build a kubernetes cluster and I’m very happy with them.
The only thing that made me buy additional hardware was the need for 10Gb Networking and more internal storage, which I couldn’t realize with my NUCs. I also learned to love the IPMI feature of server motherboards, that NUCs don’t offer afaik. I would recommend to use a hypervisor like proxmox which makes it easy to spin up new servers inside virtual machines - this way you don’t have to re-install your OS on the NUC everytime something goes wrong or needs to be upgraded.
Generally a NUC is a great device for a homelab, especially if you’re just starting out!
Since you’re also located in germany, I’d like to share a site I found when I was looking for my own router based on OPNsense: NRG Systems. Some of their models use pretty old hardware, but I got the IPU651 with the 19" chassis and I really love it.