The most important part of all this for him was to make sure that he took control of this place and use it for his own benefit.
More than the manuals, techniques, and treasures of this place, what Eric deemed the most important was the space of this, and the structure of this Nightless Stone City.
While all those things were certainly important to him, and for his future, the necessity of having a secret base to train and grow his corps was definitely the most pressing issue.
It wasn't that he hadn't thought of using the outside world for tempering and training his forces, as he had already set up a few small training camps.
But they were still only the kindergarten structures for him, and he couldn't use them to train his forces behind a point.
Furthermore, he couldn't be relaxed after giving them high-level manuals and techniques, as that would be more like giving them troubles rather than opportunities.