The real question is, if you're expanding, what do you currently use? Do your security cameras use Ethernet cables to record to a hard drive? Or are they coax and they record to a dedicated machine of sorts? If you're expanding, you'll need to know what is in place, so that you don't just add incompatible hardware into the mix.
If you can post some details, I might be able to give you some basic guidance. I used to code a Point of Sale system that included security cameras going to a NAS hard drive. I won't know everything about cameras, but maybe I can get you in the right direction.
What make/model are your current cameras?
How are they powered?
How do they send the video feed to be recorded?
If you use a hub/switch, are there open ports on that device?
Can you view this data remotely, or only while in the store?
Does a company currently run/manage any of the hardware in place?
