Tom, I actually did do it over once already. It wasn't about the technical capabilities, just the number of cameras. I started off with an 8 channel system, but later bought a 16 channel. I'm using all 16, and have plans to re-employ the 8 in the future to watch the aisles.
Seeing as how you and I have similarly sized layouts, and lots of places that need watching, you should really plan out where you think you'll need coverage.
I'm just using the cameras that came with the kits. I'm not sure what you can see at distance, because my cameras are mounted in fairly confined areas. The larger the image, the more you should be able to see. Most systems will allow you to either have all cameras visible at once, or select which camera to view. My screen is 55" and I have all 16 on at once. It produces an image large enough for me to see what I need to.
It just takes a little work to figure out the exact placement and aiming of the cameras to capture what you need. It might not be a bad idea to buy a system with a larger hub than you think you need, so you don't end up with two like I did.
