Sounds like you have a beautiful rosemary plant! I would be careful about giving it a big trim in winter. While indoors, trim any branches growing longer than the surrounding ones to keep the shape neat. If there are spent flowers those could also be removed. Also, cut out dead and damaged branches, cutting back to the nearest healthy portion of the stem with sharp shears. Once outdoors, trim back the entire plant by about one-third to control its size and shape. Start with branches on the edges and work your way inwards. Trim into the succulent green stem portions, do not cut into the woody bottom section of each stem. Continue to remove any dead, diseased, damaged, or dysfunctional growth. Throughout the summer, prune back overgrown stems to maintain shape and size. Minimize trimming near the time you take your plant indoors in the late fall, to allow it to regain its strength for the winter. As you surmised, rosemary is an evergreen perennial (in some climates!). It should not be pruned hard back into thick bare word. Good luck!