Update to item 2)
I *have* located the Buying Guide ( http://www.adobe.com/products/business-catalyst/buying-guide-subscriptions.html ). My guess is that I must upgrade to the webCommerce option to make all of this possible. That's okay by me... Any guesses where I'd have to go to actually give Adobe my money??? There doesn't seem to be any way to actually pay for the upgrade in service, just information about what it includes and what price it would be if you could theoretically purchase it.
True, there is no upgrade path for the Free Cloud sites at this time.
You need to start the site from your partner portal in order to set the plans the you want. However having said that you won't be able to add eCommerce with Muse yet. Muse just isn't at that point.
You would need to create your site in Muse if you like and then move to Dreamweaver to add further functionality. This would indeed break compatibility with Muse though.