The usage I mentioned was purely for the server & NAS, not for the other two systems I'd be running.
As for your first point, I build from source pretty often, so this CPU is definitely the one I want. I'd buy it for myself, but in the name of budgeting, I'm opting to split it across 3 systems.
I also like to mess around with ML (primarily object recognition and recreation), so the memory is also a given and it's insanely cheap compared to what it used to be. I spent $140 on 16GB around when DDR4 came out and now 32GB sells for around $160.
To top it all off, I already have a very large archive that'd use most of the 4TB anyway. It's just a speed upgrade from the HDDs I use in my current DIY NAS.
I do transfer very large files over LAN relatively often. Mostly media and game installations. I'd opt for 5Gbps to max out the 2.5" SSDs, but it's barely more expensive for 10Gbps. I'm also an avid proponent of future-proofing.
Yes, I don't entirely understand Unraid yet. From what little I've seen of it so far, it's definitely interested me. I'm fine with it being complicated to set up as I do have a decent amount of experience with VMs already and it seems pretty similar. I just wanted to know how well this specific setup would work and if there were any tradeoffs.