A very small question:

I'm doing the Telvanni quests and I'm skilled and chored enough to be named wizard. I know that the next rank could be Magister, which leads to challenging Gothren and becoming archmagister independently from my skills at that moment. I'm also doing the main quest, but I'm at a really early stage, so no way to become Telvanni Hortator in the near future. If I kill Gothren and become Telvanni Archmagister, will I be able to subsequently acquire and do the Telvanni Hortator quest, or should I get both quests in my journal before killing Gothren?

If you know the answer, feel free to spoil away, It's my Nth playthrough so I know pretty much every coup de theatre...

If you're the top member of a Great House, you'll automatically be named Hortator as soon as you ask the right person. You get the Hortator item, but not anything you would've gotten by convincing the councilors (in this case, Dratha's scroll of summon Golden Saint).

Speak to Master Aryon, he will tell you since your Archmagister you automatically are made Hortator.

Yes, the leader of a great house can just name themselves hortator.

Caveat: if you are at least a Master of House Telvanni, and all the other councilors are dead, when you discuss the matter with Nibani Maesa, you will declare yourself Hortator.

If you aren't at that rank yet, Aryon needs to survive, at least.