I would set up a media server in the old case that fits your drives but set up the game servers on the lenovo.

Plex is fine for people that already have it set up but since you’re starting from scratch why not start with the free one?

Have you already bought a HexOS license? You can do more with Proxmox or TrueNAS for free.

Paying taxes for something doesn’t mean you own it. Even if it did, I doubt the businesses fighting housing today are the same ones that paid the taxes 45-70 years ago.