wdoellefeld is right to suggest supernetting. It will give you the flexibility to do what you want. You can also phase it in over time WITHOUT having to do a mass change overnight. Here's the simple solution:
Assume IP of 192.168.0.0/255.255.255.0 (i.e. /24) You have IP's from 192.168.0.1 to 192.168.0.254 available. Not enough. You want to expand it out to, say, 1024 addresses. So you want a 192.168.0.0/22 (255.255.252.0) = 192.168.0.1 to 192.168.3.254. Plenty.
Change all server's, router's, switches AND printer's subnet masks to 255.255.252.0.
If you want to stick with static IP's then any new PC's you should add from a static pool starting at 192.168.1.1 upwards. Try and stay away from giving out the 0 or 255 addresses as some systems get very confused.
Now, all that you are restricted on is that any of your old PC's will not be able to talk to your new PC's. Change their subnet masks at your leisure. Generall 200 pc's in about a week or so.
Now, for DHCP. This is an area which is fraught with difficulty. I love DHCP as I can add options and change things at my leisure. My laptop users also can go to different offices and not have a problem. So how to protect against rogue lappies? The best way is to source all your laptops from the same manufacturer and restrict IP provision to their MAC address prefix only. But, users tend to like the laptops they get at work so will get the same for home. Problem comes back. Add in the switch port security and you are laughing. Here all ports are disabled. You enable a port as it is connected to for the first time. Then you immediately lock down the port so that ONLY that MAC Address can appear there. This is network nazi time but it is secure.