I currently have the Optik 4K PVR and 4K wireless box, if I purchase an older HD wireless box from someone will I be able to connect it? will PVR's set to record to the 4K PVR transfer to it?
You should be able to add it to your network, and be able to play recorded shows through it.
I'd look to see if renting from Telus is a better deal, as you continue to get support for their equipment.
You will need to contact Telus to activate the box. Once that's done it should work. If it's a non-4K box you will not be able to use any of the 4K services.