Build Rig 1070 4x but update possible

Hi All !

Noob on this hobby ^^
Im looking for a rig with 4 x 1070 but update to 6 possible.

OS: win 10 x64
MB: TB250 isnt available, im looking for a mb ( 100 - 115 euros) any idea?
GPU : MSI GeForce GTX 1070 Gaming X - 8 Go
RAM: 2 x 4 GO maybe only 1x
CPU: Intel G3900
RAM: SSD PLUS SanDisk SATA III 2,5" 120 Go
PSU: hx1000i but maybe too much for 4x 1070 and maybe 6x ?

feedbacks are welcome !

thanks,

tim