Before starting make a IP number plan for IP4 and stick with it.
We will use a C-network with the numbers 192.168.y.0. Y depants on the manufacturer of the router, but can be changed. This is important when you want to access your network over VPN. So use an non-standard value for y.
If you need more than one subnet, use 192.168.0.0/24 for the backbone. You can than attach the subnets to this backbone. Be sure that you use 1 Gb/s for the backbone. The router to the WAN is on this network.
For the gateway (router) standard IP is 192.168.y.1.
On some routers the default is 192.168.y.254. If possible change it to 1.
For a alternative route use 192.168.y.2.
Inteligent switches and wifi-repeaters can use 3 to 9.
A server needs a fixed IP-address. I use the range from 11 to 19 for the servers named server1 to server9.
Network printers also need a fixed IP-address. I use the range from 21 to 29.
Camera's and other type of equipment that works best with fixed IP can use the range from 31 to 49.
Use the range from 51 to 249 for workstations with DHCP IP addresses.
By using a planned IP plan for IP6 we can forget the problems when we use the MAC-address for the hostpart of the address.
For the gateway (router) you can use fe80::1 if you can change it in the router. This can be done in every lan-segment. FE80 adresses are not routeble.
A server needs a fixed IP-address. I use the range from ::1:1 to ::1:ffff for the servers named server1 to server65535.
Network printers also need a fixed IP-address. I use the range from ::2:1 to ::2:ffff.
Camera's and other type of equipment that works best with fixed IP can use the range from ::3:1 to ::3:ffff.
Use the range from ::f:1 to ::f:ffff for workstations with DHCP IPv6 addresses.