Keep 8 in FTs, they absolutely do drop with 0. You might argue they don't drop enough to be worried about, but I saw multiple players drop a shown letter grade when I tried 0. Sure they were probably right on the cutoff already, but I don't want them dropping since they improve so slowly (and I can't tell how much they're dropping!).
I use 0 for everything else. You can even use 0 for non-FT ratings when they're just close to maxing out. Depending on the player, I might drop to 0 when something turns red and focus on other areas. You will sometimes lose a point or two over the season if you push the envelope like that, but sometimes that's ok.