There will be some changes in the API related to mappings that we will introduce with an article in a few days. You can start extending the starter kit, but if you really want to be on the safe side you can focus on widgets and templates that don't persist data in the database until we release our Q1 version next month. Of course there will be an upgrade path in terms of the API but you will need to dedicate some time for that since this is not going to be automatic.
The best way is to extend the starter kit is to open it in visual studio and start building on top of it. You can always bind your project to the project manager by modifying the Projects.xml file that is available in the directory of the project manager, once you create at least one project. We plan to include functionality for open an existing project with some of our next releases, so that you don't have to use the xml file.
Excuse us for the inconvenience and the late response. Please let me know if there is anything else I can help you with.
All the best,
the Telerik team