Well, that's the case if you choose Valmark's one
problem to be supplying troops to Osterfell. (I assume that you chose Osterfell to have fealty (Oath) during its creation?) That to me has all sorts of ideas for fronts and dangers to take advantage of the fact that all of Valmark's best troops are garrisoned in Osterfell. Also, why is this the case? Is Osterfell particularly important to the kingdom or under threat, whereas Valmark maybe in a 'safer' geographical location?
If you would rather choose another problem then do so, there are some rather evocative ones on the list. In which case, Osterfell's watch is bumped to Militia due to its Oath (another ripe story hook) and Ostermark retains its own Militia too.
Oh, and I know you are just creating Valmark Nemo, but don't forget narrative descriptive tags already determined in play will update prescriptively whats going on.
Updates are both prescriptive and descriptive: if an event transpires that, say, gathers a larger fighting force to a village, update the tags to reflect that. Likewise if a change in tags mean that a village has a bigger fighting force you’ll likely see more armored men in the street.
p.214
You can choose a trade tag effect too no? One of which is a
military outpost, which would in effect counter the
offering defence option.