I'd like to apologize ahead of time if this is the wrong part of the forum or there's already a thread about this. I didn't find one, and this area seems appropriate, but I might just be missing something.

 

I'd like your formation upon entering a new area (particularly when manually resolving stronghold attacks) to be determined by your formation, not your portrait order.

 

I prefer to have my main character in slot 1 so they "lead" the group and I get their canned responses when I tell the group to do something, but I typically play squishy archers and mages so when I walk into an area with enemies by the entrance my main character has to spend half the fight running away from an enemy warrior or two.

Not possible as far as I know, you're stuck with the portrait order I'm afraid. At least for the stronghold attacks though, you could just solve that my temporarily swapping your main character to a another slot, and moving him back after. Not ideal, but it saves a lot of running around during the fight.