Black Letter flourishing is a bit different than pointed pen (Copperplate or Spencerian) flourishing. You may find
this post helpful. The link mentioned in this thread includes tips on flourishing from some of the top calligraphers in the world, many of who are referencing broad pen flourishing.
Your piece is really lovely. With broad pen, less is more is definitely the way to go.
Bill Hilldebrant's book on broad pen flourishing would be the best resource but sadly is out of print and still under copyright. Somehow, someone has uploaded a copy to scribd.com if you have a membership.
Google Books has a small
preview which is worth looking at.