Missed your second question there -- I've always just installed Ubuntu from scratch on the VM guest. I've done that enough times that it doesn't feel like a lot of work to me.

VirtualBox does have a nice feature that automates the installer, as well.

I've never bothered with the whole Vagrant thing for personal dev machines, given the low cost of spinning up a new machine, it's not worth learning a new toolchain for me. But if I was spending more than a few hours every couple years on building new VMs, it would be worth it.