Upgrade should be fairly painless. 2011sp1 and 2013 are the same architecture and so not too many surprises there. If you run VBScript tempalates, you'll need the legacy pack since 2013 no longer requires COM+ for Templates or APIs.
You'll need to re-compile any C# TBBs, Core Service, Event System, or other custom applications that rely on Tridion assemblies. There are no breaking or removed APIs, so this is a low risk operation.
For the cloud, you will need to use 1 instance of Win 2012 Server for the CMS and another instance for the DB. I have had fairly good performance with the Amazon Large instance and this would probably be OK for Dev/Test. Medium instances are a bit too slow.
I have also had fairly good performance with a medium Azure instance. Seems to perform a little better than Amazon, no idea why.
Finally, follow a good security plan for accessing the cloud servers. Typical meausres include whitelisting certain IP ranges or addresses. But, this applies to all cloud systems, not only Tridion. Good luck and make sure to follow the upgrade guide in the Tridion Live Documentation.