So when I ask Let’s Encrypt for a cert, I ask for *.int.teuto.icu instead of specifically jellyfin.int.teuto.icu, that way I can use the same cert for any internally running service. Mostly I use SSL on everything to make browsers complain less. There isn’t much security benefit on a local network. I suppose it makes harder to spoof on an external network, but I don’t think that’s a serious threat for a home net. I used to use home.lan for all of my services, but that has the drawback of redirecting to a search by default on most browsers. I have my tailscale exit node running on my router and it just works with SSL like anything else.
I think my instance has been growing at about 30 GB a year. I think if you set it up to not rehost the pictures, you can keep the whole thing in the handful of GB range.