I got 2x 290 and 1x 7990 and a cm v1000 psu , 2nd gen g630 + board that can support these cards +hard disk etc
Will these cards run fine at stock voltages and settings or will my setup require more power
This should be enough.
1 more thing there will be around 6 120 mm fans also in the closed rig
and also will it be better to use 1-2 the cards without risers or all cards on risers
if you're in closed case rig you might not need a riser, other than the 3rd GPU, its your own taste and design, either way it should work fine.
ambient temperature around here is ranging from 14-22 degrees and its only gonna get colder later on .
Electricity is included in rent (within limits )
this would be advantageous on your part.