Mid Game

Upon reaching nether level resources, you will unlock an entirely new dynamic to gaining power: The Scroll Forge

The Scroll Forge is used to craft scrolls by using ink, paper, and a focus. The ink determines the rarity (and therefore level), and the focus determines spell's school.

Furthermore, intermediate spell books can be crafted using nether resources

Hogskin is dropped by Hoglins

You should also start to craft stronger armor using arcane cloth. In order to get high quantities of arcane essence, you will need to focus on raiding magical structures.

In order to continue progressing, keep an eye out for runestones in magical structures. Runestones are used to craft even more powerful armor. Class mages always drop a rune of their school.