I wouldn't worry about buying a first year gen3 either, if that is what you are waiting for. By the time the first gen 3 comes out, the issues if any with the new f150 would be solved anyway. So saying that, I wouldn't "overpay" for a 2020 model.
I disagree somewhat. Every model year has issues. I just bought a '20 with a major transmission issue that appeared due to poor QC from a supplier. Not to mention, the truck has tons of small electrical issues, and major camera issues. Being the last model year, it should be the most sorted. It isn't, but that happens on a manufacturing scale of this size.
Buy what you want when you want it and enjoy it. Fix any small issues that pop up under warranty to prevent the bigger ones. Maintain anything and it will be good to you.