Adding Cameras to My ADT System—Looking for DIY Advice

I currently have a basic ADT setup with door sensors, a smoke detector, motion detectors, and so on, but no cameras. I’ve been thinking about adding a doorbell camera, but I’m not sure how to go about it without having to deal with a sales rep coming to my house.

Ideally, I’d like to buy and install the cameras myself, but I don’t want to make the mistake of purchasing incompatible equipment. My system uses the Qolsys IQ 319 (GE), though I’m not entirely sure how relevant that is. Unfortunately, the MyADT page hasn’t provided much useful information on this.

Can I add compatible devices on my own? I’m also open to the idea of canceling ADT and switching to self-monitoring, but I’m unsure about the feasibility and logistics of doing that with my current setup. I’ve heard some systems are easier to self-monitor after canceling the service than others.

Any advice or experiences would be greatly appreciated!