Yes, it has two M.2 slots for SSDs. See manufacturer's page under Specifications -> Storage: https://www.asrock.com/mb/Intel/Z370%20Pro4/index.asp#Specification

This means that the motherboard is compatible with a quad-GPU (4x graphics card) configuration from AMD as a multi-GPU (multiple graphics cards connected together). This does not mean that other graphics cards from Nvidia will not work. Yes, an RTX 2070 can be used. PS: Basically, the mainboard does not care what kind of graphics card you install.

Yes they are.

Yes, 2 SATA cables are included in the scope of delivery. You can find more SATA cables here: https://www.digitec.ch/de/s1/producttype/datenkabel-intern-pc-444

The mainboard basically does not care which manufacturer the graphics card is from.

Yes, he is.