Hi peepo, welcome. Ulco/Dune is an enthusiastic and skilled Terragen user, but not an official representative.
There is currently a relative lack of official project-based tutorials. That's something we're working on, although I can't say we have specific plans to do something like an in-depth Mars scene in the near future. Most of our content will be more basic and general for now, building on the First Scene document, and then augmented by short-form technique-specific video tutorials. Covering use of Fake Stones and other techniques to quickly build up a complex, realistic ground look is a good idea for one of the earlier video tutorials or for a series, so I'll add that to our list and try to prioritize it, but it's not something that would be immediately available unfortunately.
In the meantime there are, as Dune mentioned, a lot of resources here on the forums, but in discussion threads, and in the File Sharing section. You can use the Search function and limit to a specific forum with the Advanced Search page here:
https://planetside.co.uk/forums/index.php?action=searchSo for example if you wanted to search just the File Sharing section.
The NWDA store and Luc Bianco's store also provide some good ready-made options. Here's Luc's in addition to NWDA linked above:
https://www.lucbianco.fr/store/- Oshyan