FYI, FWIW, we added a 22' x 26' deck sounding similar to your plan in 2018. We did it ourselves. We purchased Trex for the decking - so far so good, very satisfied, no mildew or mold problems, would do it again. Ours is on the NE corner of the house, so it gets sunlight likely half the day (which will combat moisture buildup that could cause mold/mildew concerns). One big area to address is joist spacing - follow the recommendations. For example, if you plan to run the deck boards diagonally (as we did), you need to narrow up the joist spacing. Enjoy the challenge - good luck.