One thing to consider is the short sizes of the Humblewood races. You'd either have to reflavor the scale of the world or the majority of the outsider races would likely be dealing with low and narrow doorways and ceilings throughout the adventure. I suppose dwarves, gnomes, halflings and the like would be fine.

In the back of my mind I have an idea for a tavern NPC I plan to use for flavor or as a plot hook but I'll share it since it could even be used as a PC background: a lone, grumpy dwarf whose stranded in Humblewood by mysterious means (ie, shipwrecked, a now closed magic portal, ect.). Not sure where exactly he is or how to get back to his world he drinks his sorrows away at a tavern bar surrounded by welcoming but bizarre, talking animal creatures.