Before gluing in the vertical fin stiffener, check if the pin is accesible for the gluing. I'm not looking at the plan and I can't remember precisely right now. Some airplanes have the pin forward of this piece, others behind.

OK, on the carbon wing tube set screws, a dowel inserted and glued with epoxy or CA for your screw is a good idea. It will also help keep from splitting the tube while drilling your hole.

Mark