Can Build Start with External GPU/SSD then become a CustoMac?

[BatPumpkin]

Howdy! I have caught the custom build fever. I'm new to both tonymac86.com & custom building, though I worked at a mac repair shop for a year
replacing and upgrading Mac parts.

I edit video on FCPX as a small side job on my 2012 13" MBP 2.9GHz and my Intel HD Graphics 4000 1536 MB GPU
is slowing me down. Clearly you can see by my MBP that I am not a gamer.

Due to time and money, I'd like to speed up FCPX rendering ASAP before completing a CustoMac build
by first building an external GPU -- and maybe an external PCIe SSD.

Is it possible to start by building my own functional external GPU and external PCIe SSD into a case
and later use the same case, GPU, and PCIe to create my CustoMac build?

Is there one case that could rule them all? -- or at least one to rule these three:
external GPU, external SSD, and my future build?

If no, stop me from going further down a dead end!

If yes, what do I need to get the GPU and PCIe SSD functional in that case as components?

If I had a mobo with a PCIe blade slot & Thunderbolt 3, along with a power supply, cooler, the GPU and PCIe SSD
could I create a working external GPU/SSD combo without the CPU or system RAM if I connect it to my MBP with a Thunderbolt cable?

FYI- I am aware that if this is possible, it will require a Thunderbolt 3 to Thunderbolt 2 cable adapter to work with
my Thunderbolt (1) MBP and that my dual-core rather than quad-core CPU may limit which GPUs I can use.

 

[Stork]

I would look in the tonymacx86 Buyer's Guide, Motherboard section. (See top of page, left, for Buyer's Guide.) Search on TH3.

tonymacx86 tested the Gigabyte Z270X-UD5, which has Thunderbolt 3. See Post #16 and #21.