Network with no DHCP - Adding Router to Lan for Wifi

1. We do not use DHCP on our network. Everyone has assigned IP's.
2. We have POE switches with different VLANS for our phone system.
3. In another building we want to add wireless.

I got a TPLINK router and connected the WAN port to a switch in the desired location. I gave the WAN port a static IP that that was unused in the same range as the other devices on that subnet. Filled in DNS etc. Since I'm simply using it for wireless I have no devices connected to the routers LAN ports, and I setup the wifi with DHCP using the standard range 192.168.0.X

Later in the day we had an issue with out Sonicwall VPN, where NetExtender users couldn't connect. Remote Access Error then later it simply said "Address Range Exhausted. But the VPN's address range is 192.168.200.X.

Maybe i'm going about this wrong but wondered if anyone had any advice.