In Europe, we can handle 32A on a single plug, so I just use a powerstrip with the C14 connector, to extend my UPS.
I'm nowhere near pulling that, so I'm safe. I'm at ~3A continiously, so I have litterally no reason to worry. Plus all the powerstrips are in spec for the country I'm in, so that's another 'yay I'm good' thing.
The R740 should be able to boot from an NVMe drive (whether this is M.2 or U.2).
RAM speed support depends on the CPU. From the top of my head, the R630 doesn't go further than 2400MT/s, neither do more than threequarter of the CPUs that can work in that machine.
You can put in DDR4-4000 if you want, but the machine will downclock it to 2400, because it can't go much faster than that.
And why wouldn't you want to go with ECC REG? It's cheap, there is plenty of it and you can stuff in 3TB of it. Non-ECC can only go to 64GB I believe.
Why do you want to import VMs from a different hypervisor? Why not build an 'golden image' on your Proxmox machine, and create a template out of it.
This is basicly how I create my new VMs. I keep a relatively updated 'golden image' in my library and clone that to a VM as many times as I need. To be fair, I'm running ESXi. I have no idea if Proxmox even has this as a feature.
there is a very annoying squealing sound coming from near the processor.
Welcome to the world of capacitors and chokes.
Basicly: The power delivery to your CPU is the squeely bit.
M.2 to SATA ports are available. I've seen more people build with those. But I have no idea about compatibility though.
Never used such a thing myself either. I have no use for such an adapter.
Those modules use some weird memory though: so-dimm ECC
SO-DIMM ECC isn't weird though. It's been out there for a longer time than you might think. Some professional laptops (ZBooks, Precisions, ThinkPads) have support for these.
I completely read over the part where you mentioned 'ZFS'. Yes, IT mode flashing is better for ZFS.
I try to flash firmware from iDRAC web interface I repeatedly get "upload failed"
Then try to do smaller steps in firmware versions. iDRAC does firmware version checking to make sure you don't upload the wrong one.
so can I just buy another two identical sticks?
Yes.
Do they have to be exactly the same
At least the same ranking (2Rx4), the same size and the same speed or faster.
And is 4x 16GB optimal configuration?
For one CPU, sure. For two CPUs, sure. It all depends in which slots you are sticking them. The proper RAM layout is on the inside of the lid. Check that for the proper installation of RAM.
for some reason ESXi just can't see it.
I did a BIOS power tune recently, and that shaved off 14 watts on idle.
So that's a thing you can also do.