Currently you can't rename them.
Actually you can use any cloud service that integrates with iOS. Not sure about Evernote, but I am sure it should work as well. There is a button on the import dialog that lets you switch between different cloud providers. That is the default file selection dialog in iOS, so if the Evernote developers did a good job, you should be able to select Evernote as well.
Undo history is not saved in your workspaces. This means that if you quit the app you will loose your undo history (not only when you export it). But very soon we will add a feature that will let you modify your designs without having the history at all. Stay tuned!