Thanks, I tried it but could not register with for forums for whatever reason
BWHQ shut down their forums. Twitter and some other places can still provide help.
I don't have any TB experience. But in Mouse Guard the missions drive pretty much everything. The goals follow missions, beliefs inform play. MG beliefs are usually a little simpler than BW (again, no TB experience) so I would follow the "what you fight for" and look at the examples in the book. The premade PCs are handy for checking out beliefs. What do the mice really fight for? Make that a belief.
Almost anything could be made into a MG mission. Find a spy, defeat/drive off a threat, deliver mail, escort someone, bring medicine, arrange a trade deal, find a new path between towns, repair/upkeep the scent border (super important or big threats like wolves will enter the territories). The world has a lot of frontier-ish, with paths and things being difficult to maintain. The wilds push back on the mice, and being mice they cannot beat them. Instead they use them to have paths with lots of cover from predators and shelter from the weather.
You can fairly easily up the stakes in MG, rather than mail delivery, there are some remnants of Midnight's army (from the comics) and they've become bandits. You need to drive them out of the territories. Mice pirates, or add a bit more investigations with mice going missing from town and a dark cult having some fowl deal with the Ferrets of the Dark Heather. You can send the mice out past the border to the ruined towns to the west that were destroyed by ferrets in search of some macguffin or another to help Lockhaven or another town.