I was thinking about hooking one up to a GPS module to run a local NTP server

https://blog.networkprofile.org/gps-backed-local-ntp-server/

Since i’m already running it otherwise, i’ve been running stuff through Home Assistant and using lovelace dashboards.

Can you enable multiple vlans?

The switch on its own will do nothing for you. It’s only useful with a router that supports VLANs

Unfortunately in your situation you’ll need to replace your current router-modem combo with a dedicated modem, a commercial router (if you don’t want to build your own linux one then EdgeRouters seems pretty good value for money) and a managed switch.

If you want to keep it wired then you’ll need to put it on a separate VLAN from your other devices. A VLAN effectively allows you to create separate ethernet networks over the same physical network. We use them at work to keep factory hardware separate from office hardware and I use them at home to keep a vpn open for streaming geolocked content from another country. Traffic between the two VLANs has to be routed just like it would if they were separate physical networks.

I have an Edgerouter POE which has a small built in switch and supports VLANs so I can easily dedicate a port on the switch to a particular VLAN. In my case I route that traffic through wireguard, but in your case all you really need is setting up NAT for internet access and not route it with your other VLAN.

Any commercial grade routers support VLANs, i’ve seen it on unifi, aruba and fortigate and have never heard of it not being supported.

As others have pointed out, if you have a switch between your TV and Router then that’ll need to be a managed switch that can trunk the vlan code back to the router, otherwise all the traffic will be comingled.

Other thoughts:

You might be able to arrange your IPs to sort of fake it. If your router is 192.168.1.1 and you make the TV be 192.168.1.2. Then you could give your TV a static IP configuration and tell it that it’s subnet mask is 255.255.255.252. Then it’d only consider the IPs 192.168.1.1-192.168.1.2 as being in it’s local network and if it tries to access something else on the LAN then it’ll send it to the router for forwarding.

I’m not sure what your router would do in that situation, but it seems unlikely it’d manage to forward that packet. You’d have to avoid putting any device on 192.168.1.3 (as that’d be the routers broadcast address) but I think you could probably make that work. It’s not really secure (as anyone that compromises the TV could change the subnet) and it’d still be possible for devices on your network to send UDP packets (but not get replies from) the TV. It’s also not really extendable and you probably can’t get a second TV to work like that (and definitely not three), but it wouldn’t require switching to commercial routers.

About 45W for my router, fiber endpoint, switch, three wireless APs and a Pi4 running Home Assistant. I’ve got a synology running separately that I suspect uses more, but I haven’t measured it recently. Thinking about putting the synology in the crawlspace as it’s kinda loud.