Am I right with thinking that a group gets 1 lot of Activities per day?
So a group who has a speed of 30 ft will only get 2 points?
With Forests having a cost of 3, does that mean they have to spend 3 days travelling to a new forest hex?
Correct, including the assumption that they're pausing along the way to conduct some basic exploration (surveying, mapping, etc.). If they're just hoofing it, I read it as they use the standard overland travel rules.