Depends on what kind of resolution the camera is capable of and how many frames per second you need for quality. If you need live feed that's about 30 fps and a rule of thumb might be about 10Mbps per camera. Are you planning to run ethernet cable to all the cameras?
Ethernet to all but one location. Would wireless work?
You're going to need a wireless bridge to carry traffic on any decent network camera. Make certain you're close to megapixel capabilitiy if you want adequate security features...remember that a good network camera is a computer, i.e., it has a MAC address and can be assigned an IP address by DHCP.