I would not run FreeNAS in your case. It's exceptional at running large amounts of disks/data, but it's not really practical in your case. I'd say if you're planning on running 6 or less disks AND you don't have a need for a bunch of IOPS, you might as well go with Synology/Xpenology/Unraid...
How many VM's you trying to run ?
Might wanna just build a cluster based on the results of Patrick's Corporate NUC project thing he's working on. For Plex, just get a machine with 8GB ram and Intel UHD630 graphics, you should be fine with a solid number of transcodes there.
HP doesn't just hand that information out unfortunately.. They want you to buy branded drives from them.
If you want wide compatibility in these machines, it's best to swap out the HP raid cards with a card that doesn't care what kind of drives are connected.
This list has been pretty helpful to me. HP Server Third Party Drive Compatability
I bought some ADATA ones on the list as OS boot drives for a G8 and all looks good from my end so far. No thermal runway or anything
Almost everyone at pfsense forums will tell you don't use it to provide WiFi. Spend $50 and get the ruckus 500 (or $120and get 3 of them). It'll be stable and much easier to troubleshoot down the road.
What's the model on just one of those sticks so I can try and find some? The ones on the supermicro tested list are pretty hard to source for a reasonable price.
EDIT: NVM, found it: