About those butted seams. the contractor should have put a piece of flashing under the seam, there probably should have been some flashing on the corner posts and the window trim as well. If it is flashed properly, then there is no need for caulk, but if the flashing wasn't done, that can be a problem. With the thick siding that you are using, I still recommend against any caulk, but look into log home construction for proper chinking of any gaps. The new chinking, done properly will outlast any caulk and will not split and crack letting water in.