Wild turtles in a 29 gallon tank?

so i found the cutest lttle baby turtle in my driveway as big as my thumb so i brought him in bc he wasnt gonna have much of a survival rate so i need to figure out how to care for it i plan on having a rock structure on the surface(only half way full) i think im gonna get a canister filter for fish too now do you have to worry about ammonia and cycling? also what should i feed it since ill have to release it in the future when it's big enough that a bird cant jump down and get him (have my aunts pond in mind)? what else does he need a heater?