I am installing pre-painted shiplap wood siding over a rainscreen (1X4 strapping) How should I handle butt-joints between pieces of siding?

I have heard: square cut, caulk; square cut, 1/16 cap no caulk; scarf joint, no gap or caulk; glue (with epoxy or polyurethane glue).

What about butts to trim? 

I also need to seal cut ends. Weather is too cold for latex primer/paint and I don’t want to wait for summer.  Will a shellac based primer (like Zinser) that can work in lower temps seal end grain adequately? Is there something better?