clearance around unit?

How much clearance is required above and around the wsm? I have an area I'd like to put the unit with a low hanging tree overhead - the closest leaves and branches maybe 3 feet above where the top of the unit would be. I'm not worried about the tree catching fire, but do have some concern about the heat from the exhaust killing that section of tree.

Similarly, the other place I was thinking of putting it has vines on a block wall. How far from the wall would it need to be to not cook the vines?

It will depend on the tree, vines, and how hot you run - and whether a breeze during a cook is present - but, assuming no breeze, I think the under-tree placement would be too close. I don't think you could go closer than 3 feet from the wall - maybe 2.5 feet from the closest vines. Giving the wall and the vines a good spray with the water hose before firing the cooker, and maybe once or twice more during long or high heat cooks, would help immensely.