Hatchlings most likely would need smaller tubs to suit them, since they more easily feel insecure in large places. If you clutter up your large tub with fake leaves and multiple hiding spots, it would work.
Females take 2.5+ years to mature, or even longer. Better to wait for a female to mature than to breed a heavy but young female too early, which could result in dangers that you don't want, for both the female and the possible eggs.
Males can be bred at ~1 year old and at least 700g. Some breed them smaller and younger, but general consensus is that it's safer to breed at least at this age and weight.