are the gateway, subnet, and server port used at all for lan?
Gateway is necessary only if your device should have Internet access. Subnet is necessary but you probably can live with the default 255.255.255.0 because it's used by all home devices. Server port is necessary too as the client will connect to that port and the server should know about. For a web server it's usually 80.
[can i still use html to make a gui?/quote]
Sure! Nobody will hold you back doing it.