Hi bhirschi and
I love lavender and have over 60 plants in my zone 4b perennial beds. I wouldn't cut anything until after blooms are done. Enjoy the lovely pollinators that come to visit, the delightful scent, and the colorful show. After blooms are spent I do trim only the bloom stems off. That way, especially in your zone, you may get a second bloom in late summer. In late fall I give my gang a nice, shaping trim - forming a foundation for even growth for next year. I use an electric hedge trimmer.
I think you can't have too many lavender.