I wouldn't use eco earth. It gets stuck on their feet and dragged all over. Go with repti bark.
I would personally go with a 6qt shoebox, or a 20qt plastic bin if it's older than a hatchling (2-3 months of age).
I wouldn't use eco earth or repti bark. Especially with a new gecko, it's best to use paper towels. There's no chance of impaction and you can easily monitor to see if the gecko is pooping.