Offtopic but the app in devuan called aqemu is a nice starting point to learn about virtualization away from virtual box which is mostly proprietary software, so not free. Ive successfully used it to run all kinds of setups from openbsd to  windows xp , windows 7 and alpine linux etc. Ive even managed to rsync full backup an alpinelinux system from a qemu session to a usb stick with encryption.

xrandr does not stick. Keeps getting reset on reboot

xrandr is not supposed to persist between reboots. Either put the command in ~/.xsessionrc (where it will be run every time the graphical desktop is started) or create an X.Org configuration file to do the same job.

I don't use Virtualbox but I know that Devuan will automatically resize the window if it is a guest under QEMU/KVM. The QXL video drivers and spice-vdagent are all that's needed. Have you installed the guest utilities? I can't remember what they're called for VB.

I am having two problems

1) xrandr does not stick. Keeps getting reset on reboot.

2) shares are not accessible. How to enable/start?

Mouse copy/paste are OK.

Thanks