3 toed box turt care

[Lrptls]

i myself dont know alot about box turtles but i am researching them to help my friend. he has a female three toed and i do not think the cage set up is right, plus her eyes look like they may have an infection in them.

i was reading about the substrate, it should be a moist substrate, should the whole cage be full of a moist substrate or just most/half. right now he has pebbles.

i also read they need to be able to get into water. his turtle does not have a very big water bowl, only about an inch or so deep. his turt is about 6 inches, what size water bowl would be good for it?

i didn't really ask what he was feeding her and i can not find much info on diet, arn't they omnivores? what plants and bugs can they be fed?

i read they do not like high temperatures, he has no light on the turts cage so its just at room temp, what temp is right for them just to make sure the turtle isn't too cold/hot?

do they need uvb light? i do not think his has one

last but not least, the turtle is housed in (at my guess) a 30 gallon tank. what size is best for a full grown three toe?