You should ask yourself a few key questions in buying a system:
- Do you want cameras installed outside, inside or both?
- Do you have specific areas or rooms you would like to focus on?
- Do you want a record of camera data?
- What is your budget for this project?
Can you install yourself or will you need a contractor?
Will this be connected to an outside source for protection?
Here is a good video on the tools you will need for setting up your cameras.