Well, you can put the network in NAT mode, I don’t know if it has any impact on Mycroft as I don’t use virtualbox myself. It shouldn’t affect anything unless you need to access something in Mycroft (ie: access with your phone and use mycroft socket, etc).
No, there is a thing called thin provision which is a mechanism of disk allocation as it fills up, but virtualization environments see the “entire” disk, I mean, if you tell virtualbox you have 20 GB disk, df -h in the guest will show you 20 GB, although your occupied disk is 5 GB in the host. This is cool because you can overprovision disks above your real storage, but is also dangerous for the very same reason, if your guest VMs grows too much, you can fill your physical hard disk.
df stands for “disk free” and reports file system disk space usage, if you didn’t formated a partition (and/or is not mounted), you won’t see there.
lsblk stands for “list block devices” and it would show you all your block devices (hard disks, usb, optical readers, etc) regarding if they are formatted/mounted or not
fdisk -l stands for “format disk” and the parameter -l makes it to show you all the partitions and formats, on my case:
sudo fdisk -l
Disk /dev/sda: 978,9 GiB, 1050214588416 bytes, 2051200368 sectors
Disk model: Crucial_CT1050MX
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x3925ad1e
Device Boot Start End Sectors Size Id Type
/dev/sda1 2048 2015196980 2015194933 960,9G 83 Linux
/dev/sda2 2015196981 2051195264 35998284 17,2G 82 Linux swap / Solaris
With those command, you will have an idea of what’s happening.