Question about AMD Ryzen 7 1800x

Yes it works...Ryzen itself is a SOC and not a CPU. Ryzen itself already supports 2x PCI-X Gen 3...which means you can even use 2 VEGA's or 2x TITAN's at the same time. The X370 chipset then has an additional 6x PCI-X Gen 2.... since the fastest SSD such as Samsung 960 PRO does not use this bandwidth at all, you could theoretically even connect 6 such SSDs if so many slots were available on these motherboards.

Most AM4 boards with X370 chipsets (Enthusiast) support a maximum of 2-3 m.2 hard disks. As a rule, one Gen3 and one Gen 2. At the same time, however, certain PCI-E slots are switched off. With the ASRock Fatal1ty X370 it looks like this:

2 x PCI Express 3.0 x16 slots (PCIE2: x16 mode; PCIE3: x8 mode)*.
* Supports NVMe SSD as boot disks

1 x PCI Express 2.0 x16 slot (PCIE5 @ x4 mode)
* If PCIE5 slot is occupied, M2_2 will be disabled

2 x PCI Express 2.0 x1 slots

1 x Vertical M.2 Socket (Key E) with the bundled WiFi-802.11ac module
(on the rear I/O)

Storage
8 x SATA3 6.0Gb/s Connectors, support RAID (RAID 0, RAID 1 and RAID 10), NCQ, AHCI and Hot Plug
2 x SATA3 6.0Gb/s Connectors by ASMedia ASM1061, support NCQ, AHCI and Hot Plug

1 x Ultra M.2 Socket (M2_1), supports type 2242/2260/2280 M.2 SATA3 6.0Gb/s module and M.2 PCI Express module up to Gen3 x4 (32Gb/s)*
1 x M.2 Socket (M2_2), supports type 2230/2242/2260/2280 M.2 PCI Express module up to Gen2 x4 (20Gb/s)*
* If M2_2 is occupied, PCIE5 slot will be disabled
* Supports NVMe SSD as boot disks
* Supports ASRock U.2 Kit

I don't think there will be big differences between the manufacturers, as this is predefined by AMD (through the CPU) and the motherboard manufacturers cannot do anything in this area.

In other words. I would have tended to say 1080 + 2 M.2 SSDs is fine. If the third is a must, you should clarify this in more detail and check the motherboards specifically to see if your configuration is explicitly supported.
Alternatively, a larger M.2 SSD and SATA-III SSDs in a RAID (if that is at all necessary)?