And where have you searched, what have you learned prior to posting this. How much weight do you look at free oss versus non-free sources.
Also impacting your decision is whether you are in Sparky 4or 5.
Step back, maybe you want to go with kvm/qemu instead. "sudo apt install virt-manager" will install it. Read before you do that. You can do "apt -s install virt-manager" and see a simulation of the start of the install. (You do not have to use sudo to view "apt -s blah" because it is a simulation). Lots of packages - yes. However a virtual box install would also install at least 1/3 of those.
If things had worked out differently, that is the way I wished I had gone.
Also, if you are going to vm's - you might want to set up with logical volume management to span drives and change size of things. lvm is nice. I highly recommend it.
How much memory do you have? I would say 8 gb min, I wish I had 12gb. What sort of extensions for virtualization are on your cpu. I bought a specific cpu that cost a little more to obtain some benefits. "inxi -Cf" will give you those details. An I3 or I5 with the right flags will run circles around an I7 without the flags.
Xen - Sparky is the one of the last distros I would use Xen for. You want a very minimal set up, almost a command line, Sparky would work well as a Xen guest.
First stop at the Debian wiki
https://wiki.debian.org/VirtualBox#Debian_9_.22Stretch.22 updated 2018 Oct 11
"apt install virtualbox" (Backports is enabled from the beginning in Sparky4 -there is no backports of course in Testing-5)
or do you want to go with the ppa. There are people in sid and stable who prefer the ppa. If you are going to stay in a rolling release, there is good info at forums that specialize in sid- unstable Debian.
There will be a difference between the ppa or the Debian contrib binary. There is a history here in Debian, for that is where all things that will affect your vm install down the years will come from.
And definitely check out
https://wiki.debian.org/KVM
a lot of command line stuff, but there is
QuoteManaging VM guests with a GUI
Virt-manager, possibly already installed on your Sparky install. How to install is at top.
My parents finances are in a VM. Backed up several ways, but I need stability. So I researched it heavily. You should too if it is going to be important to you.