Ahh, that's a good start!
Pushing fluid through that many blocks with a single pump would be tough. I don't think it would overheat per se, it just wouldn't be optimal. The flow rate would be pretty low. If you had two pumps in series then you could do a single loop.
The "standard" is that if you run a single video card then a single loop is 9 times out of 10 very acceptable. Jump to 2 video cards and add the MB and CPU blocks in and you have a pretty restrictive single loop (which can be brute-forced with 2 pumps in-line). Optimally, you'd have a dedicated VGA loop and a dedicated MB/CPU loop. Fitting a dual-loop into a 900D = no problem :D