Is there a way to change the default first page to “Categories”? Having just the latest submissions makes it hard to inspire new threads. I presume than the disposition of threads also needs a fix.
Plus, so with many pinned posts the attention is divided too.
Done. Let’s see whether people are happier with that new default 
I don’t get what you mean. What would you like to see in this forum in an ideal case?
Yes, that’s an issue. I’ll try to reduce the maximum number of globally pinned posts and the pinned posts for each category to 2. I guess the best strategy is to have permanently pinned posts that link to the most important currently or permanently important posts within that category. They would also be the ideal entry point of new users.
Is too far fetched but crossed my mind prioritizing themes that are more general, more broad and thus open to be constantly answered, so they should be at the top. For example, in the TP area the transhumanist declaration should be at the top while news should be right under.
But is a bit too much, and pinning important topics should suffice. If by any case you want a more responsive involvement, a way to include links to all threads could be included at the pinned posts.