I have two yellowfoots, and from everything I have read, I would tend to agree. More humidity is usually recommended for yellowfoots than for redfoots. Water is used for soaking as well as drinking, but should not be too deep, as the tortoise could get overturned in it and drown. I have always heard recommendations of a wide, shallow dish, that they can climb into and get their underside wet with. You can soak them additionally in deeper water under supervision.
I feed my yellowfoots a mix of fresh veggies, greens, and fruits. I think about 20% fruit sounds right. I have heard many people say that yellowfoots eat more fruit than redfoots, but then I have heard that the other way around too. I think they both eat more than other tortoise species. Mostly I would make sure they get enough greens and veggies, and they should do well as long as you don't go nuts with the fruit. The non-fruit part of their diet should be greens like dandelion and collard, and veggies like squashes, carrots, etc. There are many lists out there of recommended fruits, veggies, and greens for turtles and specifically for tortoises.
The only thing I am not too sure on is how you can be sure you are feeding the enough. If you find a chart or anything, please let me know.
Other than that, I have recently started thinking that weighing them to be sure they are still growing well and not losing weight would be the best way. I have to get a scale for them yet though.
~Kyle