Just a holding post, really. I have been spending about 4 hours a day on this subject, and am going to have to scale down my contributions, regrettably.
Which annoys me, because I am like a dog with a bone, where problems are concerned
. Regrets to the OP.
It seems that a lot of these dramas revolve around the Linux 4.13 kernel, and you can establish this for yourself with a Google search using keywords "virtualbox linux kernel 4.13".
It affects VirtualBox 5.0, 5.1 and 5.2, and I have tried it over two (2) LInux Mints, an Ubuntu, a Peppermint 8, and others which are on my system.
I went as far as downloading an alternative, VMWare, only to find that it, too, has some dramas with 4.13 series and spits out an error about insufficient memory (I have 8 GB, and swap of 4GB enabled for this exercise). There is a workaround for this, but it is complex.
I have enclosed a PDF of some of my workings, be warned it is 7 - 8 pages, but it shows some of the steps I was taking, for those interested.
Bottom line is that you can get VB to work if you "dial back" to kernel 4.10 series, but I am not aware whether you would then miss out on any security patches.
Also, note that with the 5.0 series of VB, you need to have virtualbox-qt package installed as well, for it to work properly, which is not always clear with the install process.
Cheers
Wizard
enc