Hi! Thanks for your questions, and sorry for the late response!
You can think of the river structure as a pointcrawl in which progression/exploration on a larger scale is only possible via boat. So, yes, they are expected to get out of the boat at certain points of interest, but in order to continue exploring, the rules encourage that they get back on the river in order to reach the next location.
As for the facilitation of "land based" encounters/exploration, you can treat it as any freeform/rules light adventure game, such as tunnel goons, which inspired this game. The rules are so simple you can just play fast and loose with it (that's how i always do it anyways, and it's worked out pretty well!)
And yes, you are correct about fighting unarmed! THey can still fight, but without a weapon modifier
I hope this helps :)