I have worked with and bred this species in the past although nowhere near as extinsively or successfully as some others.
My smallest producing female was right around 6 inches.
Males will start mating attempts much smaller and one male had definite success once he surpassed 5 inches.
When you get your first egg I think you'll be stunned. The size of the egg is quite large given the size of the animal.
Good luck with them. They are fantastic little critters.
Yes one egg (rarely two). No worries though becasue they make up for it by laying multiple times a year.
Also note incubation times are LONG. By cooling the eggs before incubation you can possibly speed up the process but in general it took mine well over 4 months to hatch and on several occassions MUCH longer.