Your CPU and motherboard are not compatible.
To further explain, Z370 is LGA 1151 v2. It was made to have a different pin layout than previous LGA 1151 CPUs and sockets. So the only CPUs compatible with Z370 chipset are 8th-gen Intel. G4400 is 6th-gen. You'd need an i3-8100 to be compatible. Which may be worth it considering motherboards that support 6-GPUs for 6th and 7th-gen Intel are hard to come by these days.
This.
Also, get a proper PSU. Dont' cheap out with shit garbage and then rig up molex to pcie adapters. A bad PSU will/can destroy your components and will be inefficient which cuts into your profits. Power is not something to fuck around with or cheap out on. Get one 1000W good PSU and sleep easy at night. Read johnnyguru.
Thank you. Is there a PSU you can recommend that can feed 6 GPUs?