Are there any rules on what IP Address to give a router? Does have to be the first or last IP (besides the broadcast/zero subnet)? Is it just a best practice so you can expand the network if needed?
It's your network, make it what you'd like. I always make them the first useable IP address. I think the most important thing is to be consistent, so you know where they are. I have a customer that assigns all of their routers an address in the middle. While that is a bit odd, they always use the same address. So they always know what the routers' IPs are.