You shouldn't wait for 12. They will be lots of changes between versions (espcially with how Kentico supports MVC). You can check out the MS1 Beta and learn from the milestones (https://www.kentico.com/product/roadmap). DO NOT use the beta for development.
The upgrade details are unknown at the point, but similar to current upgrade process for Azure app service, you will need to download the site to local environment for upgrade then upload back to Azure.
As far as training for content admin. For MVC implementation, admin only need to learn how to manage structured content (page type pages) and media library, as to the portal editing and widgets are not available to them. You may want to consider a custom training for them if you have a group of users.