There are no official templates available. However, there are quite some people interested in creating their own design. One or the other has copied already the standard worker as seen in different videos and here and there you will find a qmo-file for download (e.g. here my interpretation).
Regarding mods, you will not need to get them “approved”. Radiant is planning to offer some kind of repository where mods can be stored and found. I could imagine that there will be some rules ralated to this official archive, e.g. that offensive mods will be not allowed. However, nobody says that you have to store your mod there, so this is far away from an approval of every single mod. The devs also do plan to make the implementation of mods as simple as possible. They plan to provide tools, so that modders do not need to handle every single bits and pieces of coding. How far this will go… let’s see. I would expect that you will need to add some code her and there and create different files. This video gives the best insights we have into modding.