well a 25 gallon is enough for 3 with plenty of room, so in a 75 i would estimate 9 if divided right.
That is just a guess as I have never had a 75 gall tank.
you think the floor space of 24in. x 17in. is to large for 1 gecko like juvy one. coz that is the half of my glass tank. or maybe ill go for 20in x 17in. i dont want to throw away the glass tank. one more thing a rubber mat is safe to a gecko coz i like to cover the silicon sealant i use in crack in middle of the tank the after i put the rubber mat i'll put a news paper.