80 for the cool side and ~90 for the warm side sounds good. Just make sure cool side doesn't go below 75. Anything below 75 will give your snake a respiratory infection.
Humidity looks good too.
For a baby. You might want to use tighter hides and have more general clutter in the tub. Babies are prone to stressing out in enclosures that feel too open. So just wad up some news paper or paper towel in there.
Your tub size is generally what would be used for an adult.
Babies do very well in 6-15 qt tubs(shoe box size). But your tub will work as long as you make it feel more secure.
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