Has anybody successfully made a multiplayer host using the game only with a Ethernet connection to their router/modem?
I would love to hear how you did it, or if anyone knows where a video is explaining the procedure, that would be great too.

Very easy create a server in game or using the dedicated server (dcon)and forward the ports on your router and windows firewall.

Just noticed if you mean local network stick the ip in and away you go.

yes

open up your router settings in browser, usually opens up when you type 192.168.1.1 in the address bar
depending on the manufacturer of the router, there should be a menu with options listed, find option named "forwarding" or "port forwarding".

do ipconfig in command line to get your local ipv4 address, open up the forwarding menu and add a new rule with the desired port you want to use for the server(default lfs port was 63392) and your local address with both TCP and UDP protocols (you might need to make these separately), save settings and reboot router. should work.

if your server doesnt show up in master server list, that's usually a sign of ports not being forwarded.

try it with your firewall disabled to see if its due to the firewall blocking any incoming connections and if so then within your firewall settings set a rule to allow, as other have also said if this did not fix the problem then it could very well be your router settings (built in firewall/port forwarding ect)