I'm starting to use my Raspberry Pi 4, connected to 1 SSD & 1 HDD, as Samba server & Resilio Sync. Is this considered NAS?

well to be fair, i did not recommend my build to others. this is simply what i built for myself. its my first time, be kind    but yes you are right, probably overkill. this was simply a diy nas project of mine for homelab. rather than buy a prebuilt like synology, i wanted to try something like this for once, also a rack nas build rather than tower (i got 4 of these already which i am phasing out   )

but i had future uses in mind, maybe convert it to a desktop gaming rack by adding graphic card. maybe use proxmox then i can setup vms for different usage (1 for truenas, 1 for OS e.g. windows or linux desktop for gaming but then for that use case, maybe the ryzen 7900 would have been better since more cores and threads to share compared to the ryzen 7600. even wendel recommended it in leveltech1)

however this mobo is a pcie 4 (not 5) despite being an am5 mobo. so it has it's quirks. would i be able to later move a RX 7800 XT nitro plus to it in future? even if i remove the middle bay to hopefully make space for it? i dont know.

but a rack case that may allow for big graphics cards is this one

https://www.sliger.com/products/rackmount/storage/cx4712/

they have more cases. some allow you to install the graphics card horizontally using a riser rather than vertical. This solves the issue where there is a height issue where u cant fit the power cable connector.
example with graphics card installed

if i could have done things different, i could have gotten a better rack case for a better price/value. probably from aliexpress. sliger is good but not sure about shipping and availability, or that would be a great pick (but expensive)

also my open rack cannot adjust the depth, making finding compatible rails a problem.

This would have been a much better open rack
https://www.amazon.com/NavePoint-Profession...B084T9NQF2?th=1

12u or 18u navepoint open rack. but i did not see any local stock 
This was another motherboard i was initially considering, for am4 build.
https://www.gigabyte.com/Enterprise/Server-...MC12-LE0-rev-1x

but there is special instructions to update to allow new bios. has some quirks and not enuff pcie slots to fit my stuff, so i went with the msi b650 tomahawk wifi instead
this was another another board i was looking at
https://www.asrock.com/mb/AMD/B650M-HDVM.2/...p#Specification
some of these motherboards if u populate all m2 slots, it MAY deactivate 2 of the sata ports (most of these only had 4 or 6 sata port). Only the msi i got seemed didn't have that issue.

If you need more sata ports, then you'd need pcie slot to then use a hba card (IT mode) to add more sata ports. need more m2 slot, then u get the m2 pcie card (also requires bifurfaction support which AMD tends to have. u have to check ur motherboard specs first)