" I've never managed to hold a group together for any longer than, say, three or four days, as they lost interest in the process"
I wonder why....
I mean, being stuck in a tavern in the first scene of the first act for 21 days irl is really interesting!
We can endlessly banter and fight with each other!
Buddy, this isn't an open world rp, you made it a one way road with the quest thingy.
So stop it from sidetracking, at max give it a week for everyone to get to know each-other then do the time skip to the next event.