Re: caulking board and battens
the only horizontal joints in siding that should get caulked are directly under a window and up at the soffit. they have to be left open so that water that gets behind can get back out.
one thing i see all the time on homes are the gap over top of windows where the cap flashing comes out from under the siding getting caulked, and all these windows there is visable water damage on the inside.
it wouldnt hurt to set a bead of caulking behind the batten when installing over the gap between boards, this will keep wind driven rain from getting into the joint and by back caulking you dont see a visable bead of caulking
fire up the saw and make some dust