Replacing server hardware, want to upgrade from SBS 2008... what do you recommend?

I should also mention that this is a very small implementation: about 12 users, about 70 GB total user files, 30 GB of email total. The overall implementation is very low-duty when it comes to resources.

Sorry forgot the link to Microsoft's migration guide.

https://technet.microsoft.com/en-us/library/dn408633.aspx

You can use that to migrate and not have to start over on your domain.

Let's combine a couple of the above answers.  <g>.  Assuming you really do want in house Exchange.... and you may change your mind when you see the cost.... then, all with one License for Server and a capable physical server.

Server 2012 R2 installed as HyperV host.
VM 1 = Server 2012 R2 with the Essentials Role
VM 2 = Server 2012 R2 with Exchange Server installed.

This gives you RWA and PC backup and a dashboard and is licensed for up to 100 users.  Very much like SBS plus PC Backup. You will need CALS for each user for Server and for Exchange.

If you opt for O365 instead you could use the above second VM for file shares, RDS, your LOB application and/or a second DC.

Thanks. I'm wondering about the benefits of multiple VMs etc. as it is a very small office - a dozen users, all saving their docs into a couple of shared folders.

Hi:  The benefits are that you can only do what you said you wanted to do with more than one copy of Server.  Plus... VM's are easier to backup and restore.  It is a learning curve, but isn't everything?  Exchange without SBS is another  learning curve and I suggest you contract the installation and/or do some heavy research and lab testing before deployment.

That is one thing I always found odd with MS SBS. They for years have told people do not put Exchange on and AD Server, yet they do it. It is one of those do as I say not as I do things. Now SBS was an install from Microsoft so I am sure they tested it and a lot of the little things that creep up when you install Exchange on an AD server were taken care of. Your other option is to put in 2 physical servers instead of VMs but the way licensing is for Server makes it a lot more cost prohibitive. Hardware is cheaper than generally than the licensing and as Larry mentioned backup becomes easier because of the built in tools to take live backups that are fully restorable on different hardware. You mentioned your current hardware is going flaky. If this happens in the future before it is time to upgrade you can just run the Virtual Hard drives off to external storage. Import the machine and fire it up on something else the with Hypervisor without having to worry about changing NIC Drivers and bindings and all the other associated headaches if the new server has different components.