I used to make potpourri eons ago. I like what you have so far. Maybe you could add some star anise and citrus peel. Lemon verbena is lovely. Do you use any essential oils in your potpourri? I like traditional potpourri: rose + citrus + spice. Lavender and lemon are nice together. You could use a vanilla pod, or add some vanilla oil, depending how strong you want the scent to be. Pommander balls are fun to make at Christmas, clove studded apples or oranges hung to dry. It's fun to experiment.