If VirtualBox is only showing 32 bit versions in the Version list make sure:

• Your Host OS is 64-bits
• Intel Virtualization Technology and VT-d are both enabled in UEFI (often advanced → cpu config)
• The Hyper-V platform is disabled in your Windows Feature list (start → “turn windows features on or off”)

Select bridged adaptor in order to run servers accessible from other machines. This seems to fall over when Win 10 sleeps. Suspending the VM and turning the VM controller on and off seems to bring it back.