So I basicly need:
1) suggestions for motherboards supporting 8 cards (maybe with M2 adapters)
2) power supplies that have enough cables to power on 4 RX580 GB Aorus each.
(1) This particular motherboard has 7x PCI-E slots and two M.2 slots.
-Asus primes Z270-A Motherboard
-Asus primes Z270-P Motherboard
-MSI Z270 Gaming M7 Motherboard
-MSI Z270 Gaming M5 Motherboard
-Asus Rog Strix Z270E Motherboard
-Asus Prime H270-PLUS Motherboard
-Asus Prime Z270-A LGA1151 Motherboard
-Asus Prim Z270-AR Motherboard
And
TB250-BTC+ Ver. 6.x
B250 BTC D8P
(2) Since Rx580 has TDP 185 Watt, let's calculate for a safe power needed 185x4 = 740 Watt. Only for GPUs. So 1000 Watt PSU will be enough for 4xRx580 plus motherboard and other parts, But in fact we can mod Polaris based cards for less power consumption.