HP MicroServer as home-based virtual host

I recently purchased an HP ProLiant N40L MicroServer as the basis of a small home network. Basically, I need to be able to backup a few Windows client machines and run 2-3 virtualized Ubuntu servers.

To me, backing up the Windows clients means I need the MicroServer to expose SMB-based shares to the Windows machines. I've been doing this in the past with a D-Link DNS-323 NAS with rsync. It seemed to work fine for me, and I thought I'd continue with that but use the Microserver for the backups as the DNS-323 has more limited size and capability.

To get the SMB mounts and Ubuntu guest servers, it seemed like I had these options :

1. Windows Server 2008 R2 Hyper-V
* Windows host provides SMB mounts
* Run the Ubuntu guests under Hyper-V

2. Windows Server 2012 beta with VirtualBox R2 Hyper-V
* Windows host provides SMB mounts
* Run VirtualBox guests for virtualization

3. Ubuntu Server 12.04
* Ubuntu host server provides SMB (Samba) mounts
* Run the Ubuntu guests under either
+ VirtualBox

4. ESXi Server 5.0
* FreeNAS guest provides SMB (Samba) mounts
* Run Ubuntu guests under ESXi virtualization

Options (1), (2) and (3) enable me to get the SMB mount directly from the host OS. I doubt ESXi allows me to run a SMB mount from within the host.

So (1), (2) and (3) are simpler (no NAS guest to maintain), but running the SMB mount on the host does increase the attack vector on the host. But since the host has limited exposure within my home network, I think that's acceptable.

I originally wanted to try BOTH VirtualBox and KVM under an Ubuntu host, but I wasn't able to install VirtualBox 4.1.14 on Ubuntu 12.04 (server with LXDE). I'm not sure what the problem was, but I suspect that since Ubuntu 12.04 was just out, there may have been some sort of compatibility issue between the two. I figured VirtualBox on Windows Server 2012 would give me a good idea of VirtualBox's performance.

I have a fair amount of familiarity with VirtualBox and ESXi, but haven't yet used Hyper-V or KVM. I plan to continue to use VirtualBox on Windows clients, so using VirtualBox on Ubuntu on the MircoServer would give me a more uniform experience.

Both ESXi and Hyper-V are said to be Type 1 hypervisors, while VirtualBox and KVM are said to be Type 2 hypervisors.

However, I've seen that at least VirtualBox guests have performance very close to Type 1 guests. So I thought I'd benchmark performance in my environment.

I just need ball park estimates of performance, and I'll install the guests with mostly defaults and little or no tuning, so take the results with a large grain of salt.