Hi jatt. My opion is, to have a system that works both. Normal work and the security-part. As the system will be running all day long, it`s fine to have a harddrive especially for this things. In Germany the prices are the same to normal hd. (Don`t know why ???)
And, if you will do normal business too, it`s fine to have a gpu (nvidia for round about 125 Euro) that makes a two monitor running possible. On one security-viewing, the other to do normal work at the same time. So, I`m running an Nvidia Geforce GTX 750 Ti for this. It does`nt need more than 70 Watts.
One (computer-monitor) and one television JTC-32``. If you buy an additional grafik-adapter look at the possibility it has. For instance vga (older monitor) and hdmi together.