You have options on the string ferrules if you leave them in place. Tape them up with blue tape before you work on the finish prep, then replace the tape if needed to get a good clean line when you paint. Another option is tape for prep, then get some liquid mask and paint the ferrules with it. Put a piece of tape over the ferrules then cut it close to leave them exposed with no wood showing around the edges, cover them with liquid mask, let it dry and paint.
