I would like to get a box turtle.. is a 10 gallon tank big enough? how big do they get? what do they eat?

any information or advice is greatly appreciated:)

My mom has maybe a dozen box turtles, when they go inside we put them in a large tank 10 gallons is kinda small. Maybe like 50 gallons. Right now they live outside, depending on age they are in a horse troff or in an enclosed area in our yard.

She feeds them left over apples, peaches, well any fruit we eat usually goes to them after we finish. She also buys repcal tortoise food http://www.repcal.com/Tort.htm and feeds them twice a day. Morning and evening. She makes sure they always have water as well. So far the adults have given us babies every year, and the babies survive hence why she has so many.