Hi Ian,
If we manage catch events on completing all criteria, we will be able send instant Moodle notifications to users. But because most of our current criteria use activities that don't broadcast any events (for example, activities inside the course), it will most likely be email notification. Users who get a badge will be also notified by email anyway, so that we can include downloadable version of their badge. Notification to Teachers (or rather badge creators) will be optional, and if this option is selected, a message will be send automatically when a badge is awarded.
At the moment we think about templates as just design templates. School, university, or any organisation might want to have all badges in the same/similar design with just minor differences. I don't think there will be any problems if you would like to switch to templates instead of static PNG files later. A really exciting thing we are looking forward to is a new development from Mozilla OB project that uses SVG instead of 90x90 pixels PNG files for badges. It might give us more options around badges, like dynamically adding user's name to badges when a badge is awarded, or any other custom setting... Not sure if you know, but currently OB project is still in beta, and they have lots of interesting things we would like to use that are on their roadmap 
Thank you for feedback, Ian! We really appreciate all ideas and questions from the community as they help us to make clearer a lot of implementation aspects.
Yuliya