You’ll need things produced by many of these professions to optimize your character, but you only get two professions you can do yourself. Unless you want to grind on a second character to collect all the reputation-gated recipes for other professions, you will probably need to buy the stuff you can’t make for yourself on the auction house. And if the price of the stuff you need exceeds whatever your questing and your followers are bringing in, you might want to sell some of your own trade goods or raw materials in order to finance your purchases.
Edit 20 It’s been a week since this post and a lot of people are still reaching out to me with questions which is fine. I have had a few different people reach out to me to help make YouTube videos based off this guide and more info in BFA which I’m more than willing to do. Whoever gets the videos up first I will link them here for you guys to enjoy.