I'm unsure about the hypervisor route, but in my case, I'm running Debian Sid on a 12 MiB Dell with a TB SSD. Then on top of that I'm running VirtualBox (aptitude install virtualbox). Within that app, I've created several virtual machines (4 GiB RAM, 120 GiB drive, 64M video RAM, etc). For each one, you turn it on, and it's just like turning on a physical PC (with a VirtualBox firmware (BIOS/UEFI) instead of a Dell firnware). The firmware splashscreen comes up, and complains that it can't find an OS to boot. I then load a Windows7 or 10 or XP or DOS or Debian netinstall or etc .ISO (or similar) file into the virtual machine's virtual CD drive (or a real CD into the real drive, mapping that to the VB's virtual CD drive), and boot and install that OS. Now I can boot into that OS at will, in a window (or full-screen), and have a fully-functioning second (or third, or tenth, with enough resources) sitting on top of my Debian Sid base. I can leave those VMs running, or shut them down, or suspend them, as I wish. With VirtualBox I can share a folder/partition, and/or the clipboard for cut/paste, either direction.
Not necessarily a separate partition. The virtual machine is really just a few files, but the main file is essentially the entire VM. You can move it to a separate partition, but no need. You can copy/move/backup that file to copy/move/restore the entire virtual machine, even to another physical box.
Pretty close to the same amount of time as physical hardware, with a little bit of overhead.
With VirtualBox, yes. VMWare, also, if I recall correctly. I'm not sure about other vm apps, like Qemu.