0 grams to 400 grams = 6 qt. tubs
300 grams to 1200 grams = 12/15qt. tubs
500 grams to 5000+ grams = 28/32qt tubs
1500 grams to 5000+ grams = 41qt tubs
Now, I write this to say that you can have animals that are HUGE, but will not do well in a large tub. They enjoy being shoved into smaller tubs.
I have larger females in 15qt tubs, not because I lack the space, but because they prefer to be in a smaller space, and do not eat when moved into a more spacious tub.
That's why there is overlap.
It really depends on the animal.
As for substrate, I use paper towels for babies, and Sani-chips (Aspen chips) for the adults.