Ya if you have many wifi devices then spreading them across multiple APs will help with the bandwidth load.
As for assigning IPs, think of it as this, Any devices that needs router management or QoS configurations or Port Forwarding kind of thing, set up Reserved IP addresses ON the router for those. Things like PCs or gaming consoles would use this method. Items like printers, Wired APs, cameras, sensors, controllers and some low priority Pads and Phones that don't need any router management, much internet or any, use Static IP addressing ON the device. This will free up IP reservation pool as well since D-Link routers have a limited pool. I have all my printers, NESTs, 2ndary APs and a camera set this way.