Hi Chris!
The whole operation will depend of what is your tolarence for the poor quality, as i will point to you that bandwidth utilization will depend on the frame-rate,audio and resoulation.
I believe you had seperated the zones of your premises to different groups.For, e.g. group on Gate 1,Gate 2,Indoors of airport etc.What you need is to deploy seperate switches with seperate vlans for each of them,and give limited access to them, for eg. Gate 1 users will not be able to see whats in Gate 2,etc.Obviously there will be a central node who will have access to all cameras, but they will access them randomly(they won't be accessing 500 cameras simultaneously (: )
Moreover If you are thinking of capturing the image to storage server,you have to do this seperately as i have mentioned earlier.
I would suggest that you first see what the bandwitdh consumption is for your Network Cameras.For Eg.a res of 640x480 with frame-rate 15 will take about 1.5mbps of LAN speed and 5mb/min storage.
If you are thinking about multicasting,then also the bandwidth requirement for IP Cameras will be very huge particularly for 500 IP cameras.
Hence I will suggest u to first use approx 10 cameras simultaneously and see the impact, then only go ahead.
Regards
JD