Windows Server 2016 Storage Spaces - changing or adding disks

This may be a very basic question, but we are a small company with minimal IT support, so it's left to me to figure this stuff out. We have a server running Windows Server 2016, with one instance, HV1, acting as a hypervisor and two VMs running on it - the first VM, DC1, is acting as domain controller and our main file and application server, and the second VM, BU1, is running Windows Backup Server for backup to Azure.

When I added the backup server, I had to add storage for a staging area. Following some walk-throughs, I ended up with a system that seems cludgy to me, but it's working - a single physical drive (as this was just for staging for Azure backup, I saw no need to set up RAID or other redundancy) is assigned to a Server Spaces (not Server Spaces Direct)storage pool on HV1. HV1 than passes this as if it were a physical disk to BU1, which then has a second storage pool running on that disk. It is this second pool that's seen by the backup server as the staging area.

Probably not ideal, but it works.

Note that this is just the staging area, and is entirely separate from the drive space used by HV1 itself (a small solid state module), by DC1 (a Raid 1 array for the OS and a Raid 6 array for data, all running on a hardware raid controller, and being passed to the DC1 VM directly, and by the BU1 OS (which is on the same Raid 1 array) as I didn't know about Storage Spaces when it was set up.

Now, the actual question: I've found that I underestimated the size of the staging area needed, and need to expand it. I can either replace the physical drive with a larger one, or add a second drive (though I'd prefer to replace, as I'd like to keep one empty bay in the chassis).

If I add a drive, it seems that it should be fairly trivial to add it to the first storage pool, the one on HV1, as that's kind of the point. But will the larger size percolate up to the second storage pool, the one running on BU1? Will it notice that the underlying, virtual, disk has gotten larger?

Is it possible to just replace the drive with a bigger one? I don't really care about the data, but I do care about not having to reconfigure the BU1 system. Can I, for example, shut down the BU1 VM, delete the first storage pool, swap the disks, create a new storage pool on HV1, give it the same name, and then restart the BU1 VM? Will it know it's changed, or will it just accept it? Is there another way to do this?

Please note that I don't do this professionally, so small words and very detailed instructions would be much appreciated :)

Although HV1 is running Server Core, I can use the server manager gui tools from DC1 to manage all 3 servers, or use PowerShell on any of them directly.

Thanks.