I think everyone you talk to will have a different opinion, but I think my views on this matter are pretty well within the accepted norm.
Your questions:
I wouldn't offer any potato of any kind to a tortoise. Too starchy. If you still want to do it anyway, I would use grated yam and mix it in with lots of other good stuff. Make the yam only a very small percentage of the meal.
I do this one differently for South African leopards vs. "regular" leopards. I find that SA leopards eat grass like a sulcata. In fact I feed my sulcatas and SA leopards exactly the same. Regular leopards will eat grass if they are introduced to it, but in my experience they don't like or need nearly as much grass in their diet. This issue is greatly muddled because of all the mixing of the different types of leopards that has happened in this country for decades. To answer your question more directly about grass for youngsters: Yes. I introduce freshly sprouted soft young grass to hatchling leopard tortoises the day they hatch. Literally. It is a regular part of their diet from literally day one.
No on all of the above. No need for any of those in a leopard tortoise's diet. Some might argue that those things could even do harm.