Total War: Warhammer III

This newest update made this more bearable but still I recommend doing it as your first realm. Try to hop into a portal right away, as intercepting an enemy is based on random chance in this realm. If you have a full stack, you will hardly take any casulties when auto resolving against the small tzeentchian armies running around. Always choose the option of them revealing the portal sigils and do the same with the special areas marked by the white pillar of light. That now also heals you completely.
The AI takes six turns to reach the prince, and what there portals lead to have no connection to you. So count the turns they have been in the realm and reload should you mess up. It sometimes happens that a movement brings you into contact with a teleport spot, porting you somewhere you didn't want to got to and costing you two turns.

But again, if you do that first, hop in right away and keep revealing sigils, you should easily get this done before the AI.