IF I understand this correctly, you want the following setup, please correct me if I am wrong:
> (1) 500gig HDD dedicated to Windows 7 only;
> (1) 2TB HDD with 2 partitions as follows:
>Partition #1: KAOS OS
>Partition #2: dedicated to backups only
I am not sure about the SSD, Citizen_WD seems to cover that in his post above. So I will assume 2 HDDs.
A lot depends on the BIOS of whatever brand motherboard you are using. Usually there is an option to tap an FKEY on boot and that brings up a menu giving you the option to boot into any operating system the BIOS detects. Asus & Asrock use F8. I currently have Windows 7, Windows 8.l and Windows XP on three (3) separate HDDs and I can boot into any I wish by tapping the F8 key on boot. I works really great, and I have no need for a 3rd party boot manager.
I know nothing about the KAOS operating system, it seems to be a highly specialized system of some kind, so I don't know if it will react in a standard way.