I have a tutorial on how to (reuse) fog to be used as a netboot server here: https://forums.fogproject.org/topic/10944/using-fog-to-pxe-boot-into-your-favorite-installer-images
For PXE booting you need to have a dhcp server where you can configure dhcp options 66 and 67. If you are in a home lab with a soho router then you should install dnsmsaq onto your fog server to provide pxe boot info in place of your soho router. Your soho router will still provide dhcp services, just dnsmasq will provide the netboot into.
https://forums.fogproject.org/topic/12796/installing-dnsmasq-on-your-fog-server
As for virtual box settings, I don’t know.