Migrate dhcp to the new domain controller pronto. Active Directory needs to be the DNS server in it's domains, and one way it keeps it's DNS records updated is by also being the DHCP server, and updating A records when it hands out addresses.
To make the migration with as little pain as possible, try shortening lease times on the old dhcp server to something less than a day and then waiting for a complete cycle of the old duration, so that when you make the migration change everyone will update and grab a new address from the new dhcp server over-night.
Use this as a good chance to update to a less-used range. Something like 192.168.128.0 would be fine. Yes, I know this means changing static IPs, and service entries for your domain controller and just about everything else. It'll be worth it.
You can't really separate devices vs servers. You could make an additional vlan, but ultimately devices need connectivity to the servers, and so gains are minimal. My recommendation here is to have your dhcp server either use reservations for your servers all near the front (or back) of your scope, or have an exclusion so that dhcp is not handing out addresses from a range in the front or back of the scope at all.
At 200 devices, you're to the point where you might want to think about a different subnet mask, to give you a little breathing room in address space. With the explosion in wireless, there's no telling when you'll suddenly need to support a large number of additional devices on your network. Instead of 255.255.255.0 (/24), you can use something like 255.255.254.0 (/23) to give you twice as many available addresses, but still keep everything on the same network.