How about a bit on cameras.
So, Like I said before there are two three ways to get a signal to your system. Wireless through and IP, Wired through and IP or hardwire into a video converter card.
But what camera? It really goes to your application (indoor, outdoor, secure, wide angle, night vision...
But for basic consumer selling points here are the things to look for. In no particular order...
Night Vision. The More LED's the better the night vision. Most of the chips in cameras are sensitive to Infra Red so Nightvision is easy if they have an IR source (or you have a strong motion sensor light)
Chip Size and Type. The bigger the chip generally the higher quality image. 1/3" inch is the new large size, 1/4" is general size, and smaller exists on the cheapcameras. CMOS and CCD... Yes, there is a difference, will you really care? Probably not.
Lense size. A lense size is predicated on the chip size (the bigger the chip the lense width changes to see the same angle), but here is my advice. a 3mm to 4mm is wide angle. 70 to 90 degree angles of view. These cameras can up to 12mm (25 degree angle of view and kinda telephoto) so you need to think through it. Lense quality might be important. I feel at this point you get what you pay for.
Connections. You may have to play connector jockey depending on your application. RCA connectors are common with the cheap cameras, BNC is more comon with higher quality. but adapters can be easily had.
Hope this helps
Carl