Gestation in a first breeding maybe 6-9 months but they can have several clutches from a single breeding and those may only be 3-4 months apart but usually more like 3 months apart. The more you feed her the bigger the clutches she will have.
There are several popular supplement schedules. This is the one I use Calcium with NO D3 Monday ,Wednesday, Friday every week very lightly. For adults and older juveniles I substitute a very light dose of Repashy Calcium Plus LoD on about half of their feeders two of the Mondays of the month. For babies under 6 months I only substitute one Monday a month with the LoD. I have T5 HO lights or the equivalent on all my cages and this combo seems to work well for my setup.
The reason I only do half the feeders is to limit the dose I do not give calcium that day.