DIY deck renovation turned into full backyard project

Started out just wanting to replace a few boards on the deck but then I realized the whole thing is rotted. So now I'm looking at rebuilding about 60 percent of it. Which means I need to understand joists and load bearing and stuff I haven't thought about since high school. My wife thinks I'm insane but also kind of respects the commitment. Hit me with any deck building wisdom before I pour concrete footings. This is going to be my entire summer I can feel it.