Do I need to leave one core "free" so that the host stays stable/accessible?
No. See, the "host" is a VM. And that particular master VM has a higher priority than any other VM's.
If so, can I leave a partial core free instead of a whole core?
Given that assigned core counts are all INTEGER, how would you even ENTER a non integer number?
Microsoft recommends joining the Hyper-V host to a domain. You certainly can join it to the domain of the guest DC.
Hyper-V itself does not need the DC for any Hyper-V related functions. Hyper-V will happily run and start any and all VM's without having access to the DC, so there is no chicken or egg scenario.
The domain join process is completed before ...
One of the methods of gathering information about VMs is "Measure-VM" PowerShell cmdlet. It will require "Enable-VMResourceMetering" in the VM.
The example of using it:
Get-VM | Enable-VMResourceMetering
Also, you can take a look at Veeam One Community edition (https://www.veeam.com/virtual-server-management-one-free.html) which is one of the ...
A tree indicates the VM was restored, reverted to a previous checkpoint. Future checkpoints start a new node with a new delta. Look at the time stamps in that screenshot.
Trees of checkpoints are not a long term solution. The accumulated deltas consume storage space and performance. To store a point in time for more than a couple days, use a backup system.
You can’t share block device with non-clustered file system like NTFS, ReFS, Ext3/4 or ZFS on top... There’s nobody to arbiter concurrent writes, metadata updates etc. Good story here:
So either you switch to clustered file system or use network redirector like f.e. SMB3 or NFS.