expanding the ports on your router

 

extra routers or switches?

switches.

switches on internet side or LAN/computer side?

multiple routers won't work on one modem!

switch(es) should be on the LAN/computer side of the router. there is an internet port for the cable modem only, and a number of switched LAN ports (yes, it's a switch, and you can connect the switches in a tree-roots fashion). you are allowed to have up to a certain number deep of switches there.

IP addresses...

I am not sure of this, but I think you can have a mixed environment of static and DHCP. don't quote me on that, check your manual or call your router company's support lines.

In the router you have a place where you can set up the router to assign a range of DHCP addresses, like 192.168.1.10-100 or 192.168.2.1.10-100

127 and above I think is not allowed, and 1 is probably the router. so you can have a lot of devices and computers (125 devices and computers) and fixed IPs (for workgroup printers, etc) in the address range 192.168.1.2-9,101-126 if I am not mistaken. you can set up the DHCP range of your router.

once you make the router change, everybody is probably going to need to either reboot or repair their connection, whichever they prefer.

126 may not be safe either, so avoid it.

Configuration 1

switch 1 port 5/8/16 (uplink port) to router LAN port 1 (optional)
switch 2 port 5/8/16 (uplink port) to router LAN port 2 (optional)
switch 3 port 5/8/16 (uplink port) to router LAN port 3 (optional)
rest of switch ports go to huge number of devices.
You will obviously need to determine the size of the need for your switches. no you do not need a router for your other buildings. The router is only needed in your case where there is an internet connection.

Configuration 2

switch 1 port 5/8/16 (uplink port) to router LAN port 1
switch 2 port 5/8/16 (uplink port) to router LAN port 2
switch 3 port 5/8/16 (uplink port) to router LAN port 3
switch 4 port 5/8/16 (uplink port) to switch 1 port 1 (optional)
switch 5 port 5/8/16 (uplink port) to switch 2 port 1 (optional)
switch 6 port 5/8/16 (uplink port) to switch 3 port 1 (optional)
switch 4 port 5/8/16 (uplink port) to switch 1 port 2 (optional)
switch 5 port 5/8/16 (uplink port) to switch 2 port 2 (optional)
switch 6 port 5/8/16 (uplink port) to switch 3 port 2 (optional)
switch 4 port 5/8/16 (uplink port) to switch 1 port 3 (optional)
switch 5 port 5/8/16 (uplink port) to switch 2 port 3 (optional)
switch 6 port 5/8/16 (uplink port) to switch 3 port 3 (optional)
switch 4 port 5/8/16 (uplink port) to switch 1 port 4 (optional)
switch 5 port 5/8/16 (uplink port) to switch 2 port 4 (optional)
switch 6 port 5/8/16 (uplink port) to switch 3 port 4 (optional)
... rest of switch ports go to huge number of devices in the cable jungle/harness.

I am not a mac person, but I am going by what little information is given by the apple airport extreme product page - it only has 3 LAN ports.

the cable modem (most anyt modem actually) is only set up to assign one IP address through DHCP. that is why you can have trouble putting multiple DHCP routers on 1 modem. an alternative is a fixed IP on your modem instead of DHCP. that can be set up with the cable company. but you might want to ask cable company tech support first if you are even allowed to have multiple IP addresses... If not, I recommend you try the DHCP switch setup I outlined above.