What's the best quest commendation farm strategy? Do I just have to do all the quests available or just doing specific quests fast enough?
If you're on Patreon, talk to Dunny, the purple tiger in the quest guild lounge. He offers you quests to repeat the dungeons you've already finished, and gives you a ton of QC for that. For repeating the Water Dungeon he gives you 50 QC! So, get the Intimidation buff for Wulfrick, so you won't encounter as many enemies, and just repeat the dungeon until you have all the QC you need. Can't 100% confirm that this is the fastest farming route, but most definitely the least tedious one.
Guild buffs are a thing you can get in your guild home (also Patreon exclusive atm) once you unlock the silver badge. Every 10 levels, a character gets a set of three possible permanent buffs you can choose from. Most of these buffs are to boost your weapon damage or give you new skills, but since people were really struggling with the amount of enemy encounters in the Water Dungeon, he also made one that makes dungeon runs easier.