These are all plants meant for your zone, which is a good thing.
I have most of the plants you mention-
Boxwood should only be shaped early summer
peony, hosta fern rudbeckia, salvia, coneflower, and other perenials- cut back to near dirt, mow them with the lawn mower- the only thing I would do by hand is butterfly bush- they are so hard to keep neet- leave multiple branches near ground level - if you don't trim them they get sloppy-the best ay to do butterfly bush is trim every stem to just above a split- because you'll get two branches above each split.
azlia and rhoodendorn are ideally trimed first thing in spring to maintain their shape - but that will take off the blooms. Id rather have a little less than perfectly geometric shape and significant booms with a late spring post bloom trim: you have to pick one or the other- perfect shape (as you see it) or tremndous blooms.
I should explain: The bloom buds set in the fall at the tip of the branch dormant but ready for spring. New vegetative growth starts in spring, usually branching from the same node as the flower. If you cut first thing in the spring, you'll remove the forming buds flower buds, but all of the plants energy will go into forming new branches, lower down, where you cut. If you wait until after the blooms, all of the new foliage and branch buds will already be set at the same node as the flower, and you'll cut those off. Depends on what kind of trimming you want to do. If they are too big by half - cut back on the first nice day- because you'll want a lot of branching new growth to fill in and next year will be fabulous. If it's just a trim, I always wait.. then I end up with tall scraggly bushes, so every 5-7 years I sacrifice blooms to recover reasonable size.
mop head Hydrangea should be trimmed right around frost- once its cool and the remaining flowers stat to brown. Only take the tip becasue every leaf node from this year is a new growth spot that will flower next year- so just take the blooms and any dry canes out for max display next year. Any bud at a leaf join this year will flower next year, so try not to cut them off unless you've overloaded
