Yes, you can buy any IP-based camera that can send an RTSP stream.
No, you cannot buy any GPU based hardware — you must buy the specific SKU with specific operating system, Nvidia cards, and driver software.
You need IP based cameras that are hooked together with a switch that connects all of them, with a stable internal network and connection to the outside world. If you are buying new cameras, we recommend getting 1080 p or better, even though we can work with 720. When you buy our software licensing, you will also need to buy the hardware that we recommend. You can buy this hardware from us or an authorized dealer that sells “Athena Certified” security GPU-based appliances.