1. How can you calculate how many rigs you can plug on that ?

- It's all about power consumption. You should ask about how many Current (Ampere) in your new warehouse power line. Then check back the power consumption for your rigs, so here you go. One of my friend has a mini farm with 360V power supply, and total current he could access is 60-A, so total power is 21.6 kW. All of his GPUs are P106-100, each rig has 12 GPUs which consumes about 1250W as mining ETH. So 21.6/1.25 ~ 17 rigs maximum.

2. How can I calculate what's the price of my Kw/H ?

- The letter from electricity company is quite a lot, I think you should ask them make a table which you could easily track. But as I understand, they make calculation based on several stages according to power consumption: 15,090 kWh and 50 kilowatts, I'm not quite sure but it seems expensive.