My opinion is that to increase the number of GPU on one rig is futile. The best option for me is a 6 GPU on one rig. Periodically, the rigs shut down. Also they need to serve. The downtime of your equipment is your loss. Big savings on the increase in the number of GPU in the same rig, you also get. Think about it.
That is right. I will run no more than 8 cards. If the rig is down, it just affect 8 cards, not 12 cards.