Do your wireless camera need Internet access? If not you should move them to a separate network.

But I’ve worked with more devices in a single low end router setup. It might a problem with your computer.

Both type of port sends one signal per port. At most you can only get 2 screen. You can check what is the maximum supported resolution on the gpu, and buy a bigger screen split them virtually.

Personally I rather spend the money to upgrade the gpu to get more ports or more modern port like display port which allow daisy chain with one single port.