Exchange 2010 Secondary Server / Redundancy

Hi

I'm trying to implement Exchange 2010. I have a single server, which has a typical install, mailbox, client access and hub transport roles. It is also a DC. I have a single static IP and DNS is configured for this server on the network and ports 25 and 443 forwarded on the router, all works fine, but need a backup plan if this server goes offline for any reason.

So... if this server goes offline, what is the best way to implement a second server so that can take over the roles of the first server automatically, ideally so clients can still access e-mail until the server is back online, or as a minimum just so e-mails are being recieved until the main server is back online.

I would ideally like to do this with a minimum of two machines, one physical and one virtual...more virtual if really neccessary.

I've looked at DAGs, but seems to ideally implement this, you need the DC, CAS and Hub Transport and a minimum of 2 mailbox roles all on seperate machines.

I've also thought about setting a virtual machine with exactly the same settings etc as the main server, which is just switched on when the main server is offline, and port forwarding changed and carries on as normal, but would ideally want an automated solution, if this happens in the middle of the night for example.

I've also thought about installing another phone line and having another static IP, which is set as the mail2.domain.com MX record for example incase the first server can't be reached. Or how would I do this on the same network with the single IP?

What is the "correct" way to do this?

Any advice gratefully received...