It's difficult to suggest anything without assuming lots of info. The only way to be sure is to survey the site.
Most systems are kits however they always have compromises by there nature
First look at your desired views then light levels etc. All cameras are not equal.
Once you have your chosen cameras and probably detectors look at the dvr.
Backplane bitrate, channel bitrate are things to consider. Imo you want at least 4mb/s for 2mp 6 plus for 4.
Then storage issues, hard drive types etc
There are kits but they are designed to be used for budgets not well designed systems