Anyone have experience converting from 1G LAN to 2.5 or even 10?

Going from 1 G to 2.5 G is fairly cheap these days. You can almost certainly use the same cabling, even when you’ve got only Cat.5e cabling. While you can do 10 G over copper, I wouldn’t suggest doing that, since it consumes quite a lot of power compared to both 1 G and 2.5 G. You’d need Cat.6E for reliable 10 G over copper.

I like Miniflux.

WTF?

or a domain with a random string of characters so no one could reasonably guess it? Does it matter?

That does not work. As soon as you get SSL certificates, expect the domain name to be public knowledge, especially with Let’s Encrypt and all other certificate authorities with transparency logs. As a general rule, don’t rely on something to be hidden from others as a security measure.

Try diasbling the second DHCP server altogether. You only need one, since you have a flat network.

Are you sure there is exactly one DHCP server running?