You would need to use 7 of the pcie ports just on the GPU's, so how are you powering the risers???
Splitters are fine to split ONE pcie port to two for connecting two risers to each, but anything more than that is begging for trouble.

Ideally you need to have enough pcie ports on the psu to power all GPUs and risers. In a pinch you can use molex powered risers, but do not use any molex-pcie adapters that come with risers, those are a fire hazard.
As a general rule of thumb, do not exceed 80% of the rated load on the PSU for long term operation, 75% if you dont have adequate cooling.