Thanks' all advices! Now, I am confident to build 8 pcs 1660S Rig with 1000W Power Supply.
hehe maybe 2 3090
No, 3090 isn't a good choice for those who are new to crypto mining and graphic cards, this RTX3090 should go to those who can manage the memory temp because that's the only thing dangerous about RTX3090
he did not give price for 3090. looks like 1660s getting 320$ each 4x320=1280$ and if he can get 3090 at msrp then 3090 good choice i tell you why. 1660s old card and have 6g memory but here you are getting 24g of super fast gddr 6x. and im sure 3090 will give very good results in any algorithm. maybe there will be new coin for them who knows also 3090 will not loose price in 3-4 years. as soon as ethereum explodes these 1660s will loose price very quick.