Making those small pieces could be done safely on a miter saw. You just use a long piece and cut the same distance off one end, moving the blade from one side of the center line to the other side with every cut. Also, every second piece you'd cut would be scrap, but I'd rather throw away a bit of wood than risk cutting off a finger.
That'd be best done by clamping a wood stop to the fence so that all pieces are cut to the same length.
If I were doing it, I'd cut them all a tiny bit shorter than they needed to be, nail them into place, then apply a latex caulk to fill in the gaps, and remove the excess caulk with a damp sponge so that only the gaps had caulk in them. Latex caulk shrinks as it dries, so you'd have to caulk twice; the second time to fill in shrinkage. But, after painting it would look fine.