13 GPU Mining Rigs setup for small farm

Hi,

I have ordered around 47 SA rx580 nitro + 8gb and i am planning to build a GPU mining Farm with them.

Total 5 - 13 GPU rigs
Specs rig 1-4:
SA Nitro + rx580
Asrock H110 Pro PTC
Celeron G3930
Crucial 8GB DDR4 Rams
2 Server PSU W/breakout Boards (1200W Each)
1 Evga 750 GQ Power supply
13 pc version 007 PCI-E Risers with 6pin to Sata power connecters

Rig 5:
Zotac GTX 1070 Mini's 13pc
all others same as above.

My questions are

1. Use Simple Mining OS or ETHOS?

2. Flash Bios for rx580 while they are on the rigs or do it first then install on the rig

3. Electricity in my country costs around 0.02/KW and i have 2 AC Conditioner each rated @ 2 tons, will they suffice or need more

4. Electrical Setup (2rigs connected to one 30 AMP Breaker Connection?)

5. Connect PCI-Risers same power supply as corresponding GPU in this case that means i have to connect 6 cards + 6 PCIE Risers from same server PSU. Is this right setup?

thanks for your help