|Anything that's going to be providing a service should have a static IP. This includes servers as well as network printers. So yes, statically assign your server an IP.|
Check the DHCP configuration on your router and pick an IP that is outside of your DHCP Scope. The default scope on most SOHO Routers is something like .100 to .199 so you should have plenty of IP's to choose from.
I would recommend using DHCP on the clients. I would leave DHCP running on your router. There's no need to move it to your server now or later. You definitely don't want to try and use DHCP on both at the same time.
I'm not sure why ddennis02 would advise moving the DHCP role to your server but here's why I say not to bother.
DHCP is DHCP and there's no advantage to running it on the server over running it on the router. Any roles your server isn't performing means it has that much more (in terms of performance) to offer to the ones it is.
If you don't mind me saying, your post is confusing. You tell the OP to move it and then say don't. Better you hadn't brought it up at all as you're just making a simple thing complex and it's been my experience in 15+ years of working in IT that one should always apply the KISS principle.