In terms of hard disk usage there aren't any formulas that allow you to calculate disc usage based on the number of cameras alone. You have to be able to account for the resolution and framerate of each camera, the compression type that you're using (MPEG4, H.264, MJPEG, etc), the file format you're using (.avi, .mpeg, .dvr, etc) and the amount of motion that the cameras will pick up. Though there's no standardized way to take all these variables into account, many manufacturers have hard drive calculators you can use for free on their websites, so I'd suggest looking up the company that made your DVR and seeing what they have to say.
In terms of power consumption, you'll have a little bit of an easier time. You just need to know what the wattages of your devices are (computed as watts = volts x amps) and figure out your kilowatt hours from there. There are many free online calculators for this, including this one below which I found through Google:
http://www.electricity-usage.com/Electricity-Usage-Calculator.aspx
I should note that those generally don't give you an exactly perfect answer, but should get you into the ballpark. Surveillance systems generally only draw a tiny bit of power, so don't be surprised if your answers are coming up small.
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