I agree with color (and shade) coding for distinguishing who is talking in dual dialogues, and for "already read" dialogue. Not for topic selection of main vs side quest.
I'm on board for noting the main quest/s as special in the journal, but not in dialogue; if it's in the journal you can deliberately just hunt down the main quest if you want, but color coding dialogue by 'importance' would be immersion breaking to me. A random NPC doesn't necessarily think the main quest is as interesting as their missing dog, so the importance is being assigned out of character.
I love the idea of setting the follow distance. When I had one fighter and one mage, I kept having to start the fights with the mage in front because otherwise she wouldn't be able to fireball. When I used two mages, I was constantly trying to get both characters to start a fight at the "front" and it's silly clicking back and forth and nudging them a bit.
I'd personally like an "Initiate combat rounds" button so that attentive players can start combat when they see a monster in the distance, giving time to buff and position, rather than having to get close enough that it auto-initiates.
