Stumbled on this a bit late so I apologize for dragging it back up. For those who don't know, I wrote Donnybrook so I'm willing to take the blame for anything that's unclear. Hopefully some of the clunky came from not yet being familiar with the rules and I'd like to point out a few things about characters.
1. Characters do not need to be deployed with the unit that governs their die type. For instance, if you have an Elite d10 unit and choose a d10 officer and a Recruit d6 unit and choose a drummer, there is nothing in the rules that forces these characters to be deployed with the unit. In fact, putting the d10 officer in charge of the Recruit unit raises their morale to d10. You can also stack multiple characters in a unit - say, a sergeant, ensign, and drummer to give multiple abilities to your strongest unit. It was unclear to me if this was taken advantage of in the game.
2. All characters have several advantages. All characters gain a +1 to hit in close combat giving even a d6 character a bit of swash and buckle. They also get to roll on a wound chart if injured (rank and file are simply removed) - this makes the d10 and d12 characters particularly had to take down. Finally, they do not need to take morale tests (unless attached - then they are caught up in tide with their unit).
3. It's not really necessary to include cards for drummers and other models that MUST be attached to units, but these chaps have a way of being the last to fall and it's useful to have a card for them in that event. Characters that are most useful when attached (i.e. officer and sergeant types) may need to leave a unit to preform some sort of heroic task (rescue a damsel for instance) so you need their cards to allow them independent action. I always name the characters and if they appear in recurring adventurers they tend to take on a life of their own.
On the subject of the convoy mission, I've had the opposite happen where the attackers can't seem to get their act together and the defenders slaughter them piecemeal while the wagons roll serenely on. You could probably play it three times and get three different results. A quick fix is to allow an advanced guard to be placed within 12" of the entry point and amend the attacker's deployment to read 'no units may be set up within 18" of the advanced guard or entry point A. Then be careful to deploy other units of the flanks of the wagons so they don't block their path if their card seems scarce. You could increase the move of the wagons to 6" as well, but remember with the TURN OVER card, some turns may be short and with the wagons moving every turn, their progress can be faster than it seems.
Finally I would encourage you to tweak the rules as you see fit to fit your table. I don't use faction lists - my games have always been mix and match as you go. The lists were meant as a way for players to get started and have a goal for their collections. There is nothing to stop you from using characters from other factions (maybe changing the name to fit in with your force) or simply making up your own (that's what I do).
Hopefully you'll give Donnybrook another try at some point!