I'm confused about how Upfront could work with Multisite

I'm impressed with the way Upfront is looking, and I read that it works with Multisite, but I'm just not clear about how that would. Specifically I'm confused about these points:
* Am I right that you need to go into one of the Upfront themes and then edit it using Upfront? If this is so, does the new customised version overwrite the original theme or does it create a new version of the original theme?
* Can you edit these as Network Admin? Or do you need to edit them on the Network Admin's blog? If you do this, how do you then make the new customised theme available to other blogs on the network?
* Is it possible to disable Upfront editing for blogs on the network, perhaps through Pro Sites, so that it would be possible to offer an entry level non-customisable blog?

Sorry if I've missed a manual which explains all this!