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There is an ftp tab where you can use an ftp server to save files. Its definitely possible
EDIT: Dahua Wiki: NVR/Recording Setup/NAS Recording Setup - Dahua Wiki
There are 64 channel dvrs.
Again, DO NOT DO THIS you will waste your money and it won't work, also how far away are the cameras, USB has a limited length for cable which significantly increases cost.
Well you need a VMS. Do you need to save video? If so you need a VMS like Blue Iris. If not just use SmartPss. For analog cameras you need a dvr. You could also get analog capture cards if you want to do it with a pc.
Probably best to stick with ip cameras. If you want to go really cheap use analog cameras US $6.62 |Yalxg Home Security Analog Surveillance CCTV Mini Camera Module Board Cmos Sensor 1099 1000 TVL With IR CUT Filter And BNC Cable-in Surveillance Cameras from Security & Protection on...