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Supermicro 826 is not a GPU friendly chassis if that's something you want to consider for the future. The power distribution board do not have GPU power unless you want to reuse one of the CPU power or combining a few Molex connectors. Also finding a low-profile GPU might not be easy.
Supermicro 829U however is designed for GPU and high performance. But it only accepts non-atx board from supermicro (x10-dru, x11-dpu, h11-dsu etc.). Those motherboards will have 3-4 GPU 8pin connectors to power GPU. 829U usually are cheaper on eBay (I got one recently for $130).
As others mentioned, they are loud though. I can live with my dl380 g9 in the same room, but I have to throw the supermicro into garage.
You make me worried. I hope my suggestion won't trigger your impulse buying.
Before you pull the trigger think again about the noise and power consumption:
They are loud, both the PSU and those 4 high RPM fans.
The average power consumption will be around or over 200W
This case can only support supermicro mother board and from what I researched they ends at x12/h12 . The latest 13 gen motherboards do not have this type of formfactor. Means the newest system you can build with this case will be 3rd gen Xeon scalable or 3rd gen Epyc. None of the 4th gen so far seems to fit. I might give you another 7 years or so.
For GPU it depends on what's your needs. I don't run Plex so I prefer Tesla (I plan to get one or two P40s for myself to run big data and ML). But I'm not sure if tesla is good for Plex or not.
For the PCIe options I would choose 3FH x16. I believe with 3FH you can still have two LP.
Also beware many of the PCI slot require 2nd CPU to be installed (you can check the manual).