Below are some notes on your questions.
1. Do we have a tutorial for migrating of custom editor templates?
Custom editor templates can contain arbitrary content, so a comprehensive tutorial for migrating them is impossible to create. Basically, if the editor template doesn't look as expected due to em unit styles, you can set an appropriate font size
to the editor template wrapper element, and all descendant elements will inherit the desired sizing, as before. The em unit styles should work in the same way as pixel unit styles for a "normal" font size of 11-14px. In some more specific cases, you can apply custom styles to override the Kendo UI stylesheets.
2. Which is the last version with a pixel-based stylesheet?
2013.2.716 (Q2 2013)
3. Do we have a pixel-based version of the latest stylesheet?
Pixel-based stylesheets work best with a specific font size. The Kendo UI widgets can be used in various scenarios with various font-sizes and this is the reason why we moved to relative units. We don't produce a pixel-based stylesheet anymore.
4. Can the ThemeBuilder convert an old skin to a new one?
The ThemeBuilder can create custom themes from the latest CSS only. In addition, please note that the px-to-em changes were made in the common
CSS, while the ThemeBuilder deals with the theme
Generally, creating a new custom theme with the ThemeBuilder is a lot easier than converting an old custom theme.
With regard to questions 3 and 4:
If you want to work with pixel units, you will have to create a custom common
CSS file manually, which is likely to be a lengthy task. I recommend you to only override some specific styles, if needed.
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI