I have run proxmox for several years, rely on it for many bits of house and network infrastructure, and recommend proxmox overall. My desktop also runs proxmox with PCIe passthrough for my "actual" desktop (but this is a different proxmox server from the primary VM and container host for infrastructure).
That said, I wouldn't mix the two use cases either initially nor over the long-term. House/network infrastructure should be on a more stable host than the retro-game console connected to your TV (IMO).
In your case, I'd recommend buying another PC (even an ancient Haswell would be fine to start) and getting experience with vanilla proxmox usage there before jumping straight into trying to run infra and MAME/retro gaming on PCIe passthrough on the same singleton box.
That said, I wouldn't mix the two use cases either initially nor over the long-term. House/network infrastructure should be on a more stable host than the retro-game console connected to your TV (IMO).
In your case, I'd recommend buying another PC (even an ancient Haswell would be fine to start) and getting experience with vanilla proxmox usage there before jumping straight into trying to run infra and MAME/retro gaming on PCIe passthrough on the same singleton box.