the RM1000 is the same one i have. plenty of peripheral slots for cards. As an idea, the package you get with cables will come with i believe 3 cables for molex, and a few cables for sata
use one cable for each just to be safe, expensive psu and all. so 1 gpu per strand connected into the psu

also if you choose to, the psu will come with a corsair link cable. connect it to a spare motherboard usb header, install the corsair link program and it will tell you how much current your pulling through the 12v rail.
good idea of how much power your using. for power usage, use this formula

12 x Reported current = Watts used per hour

as an example
12V x 13A = 156W

READ THIS
The psu fan will NOT spin atall until it hits 400W loads
it may never hit that amount so do not worry about it