Good Morning Charles
VirtIO does not provide for a “VirtIO Virtual Connection”. SCSI is then used (SATA is not an Option in “Virtual”, this also uses SCSI).
I also use VirtIO, which results in a virtual SCSI Controller, using VirtIO SCSI… 
Network is also VirtIO. For Servers and Workstations, I avoid using “Balloon memory”, this is never a good idea anywhere where SQL can be used!
I’ld choose Q35 as Machine Type, not the 15 years older “Default i440fx”. Q35 is from around 2008, i440fx is from around 1990!.
Tip: This can be changed on Linux easily, even after installation - not so on Windows… 
But DO shutdown the OS and start anew!
I’ld also suggest starting out with a 300 GB Virtual Disk! Keep this as single disk, until NS8 is ready to use a second disk, it will be coming
…
The Migration offers you a step by step, and you can ignore / stepover any Apps you do not want to migrate (Or do manually!).
Generally all users, groups, apps and data files will be moved!
Mailboxes are owned by users or groups, but a user can have more than one Mailbox.
VM Disk Settings in Proxmox:
Set the disk caching as follows
Only after updating and migration, (and Backup!), and everything works as expected. then you can try this
This needs a shutdown and start, a reboot will not suffice correctly!
For your System, t’s almost of identical size as mine at home:
If possible, allocate 8 cores (1 socket) for your NS8, my Proxmox here only has 4 cores (A low powered Odroid H3+…).
This is not really sensible or even needed. Even NS7 first made a local backup, then “pushed” that file to whatever Backup location NS7 was using… (Duplicity, Rsync, Restic).
Don’t forget, with PBS you can retrieve ANY file, also the local SQL Backup Dump (All of them individually!) - you just have to know where they are. Mostly under /users/APP-Name-Number/whatever).
If you do want a separate backup of the actual SQL dumps, it would best to push them to a NAS for storage! (Way more efficient!).
NAS: Mount with NFS, If you have Rsync support, use Rsync!
Depending on System and IO speed of your host, I’ld suggest to plan in about 4-8 hours for File-Server and AD together. These two always go together, and are the last to migrate.
Mail and Nextcloud generally go faster!
Post Migration
Your NS7 will still be running, now using the AD in NS8 as account provider!
This will provide users for all Apps not migrated, so can still be used until you’ve migrated all stuff you want. If you do not have any further use for your old NS7, it can be shut down (Keep it archived for 6-12 Months in PBS or Whatever!).
NS8 will now be your AD and Account Provider.
So adapt the DNS settings locally AND in AD (Using RSat).
To access the file server, use the name shown in AD:
This image is from a client server. My home server was migrated from NS7, but still during Beta phase and a bit messy in the end. So I did a complete new installation, with new AD - also to reflect the correct site (r9.). So it can’t be considered migrated. This one IS migrated and running over one year now!
On any Workstation in the Domain, use
\\NSDC-SUMA-DB012\SHARE-NAME
Note: This is a “random” Name. It’s always as follows:
NSDC - XXXX - RANDOM
Adapt as needed!
BTW: The AD in NS7 had it’s own IP, different from NS7 itself. In NS8, AD uses the IP of NS8.
Samba itself will not always react to the NS8 DNS name for mounting, but will react to the correct AD name quickly!
Don’t forget to reflect this in DNS!
A data share on the NAS, intended for Backups, as a suggestion how to structure this…
I use a 20 year old rsync script , adapted for each of my clients, and run daily to achieve this.
And yes, the master script has been adapted over time… 
All my clients (and all their users) have read only access here.
They can allocate the backup file they need themselves, and copy it back to productive locations themselves.
No Cryptollocker can manipulate any of these files, the NAS does NOT allocate any R/W permissions to AD users. The admin has a different Password than the domain admin!
In case you’re wondering about the Novell_NetWare folder:
For me, this client started out with Novell-Netware and Coaxial 20 years ago!
At first NW311, I migrated to NW411, then to NW5.1, NW6, and finally NW 6.5.
The first were native installs, from NW 5.1 running as VMs in VMWare.
The VMWare was a native install first, now it exists for archival reasons.
Neware 6.0 and 6.5 are still both available, and run as VMs (still in VMWare), and VMWare runs as a Hyper-Virtualised Hypervisor, running on Proxmox!
This is a financial services company (Called Treuhand here locally) and needs this for the 10 year legal requirement.
The matching XP Client is also available, as Terminal Server with multiple users, in case it’s ever needed.
The data and App has long been migrated to a dedicated Linux Server.
I ought to be available when migrating, so ping me for help if needed.
Good Backup, Good Luck and Good Migration!
My 2 cents
Andy