I keep 3 very happily in a 20 gal, so I would agree with the 3-4. As long as everyone has a place to hide if they want to be alone, they should be happy as clams.
Its would be good to have more hides than geckos, & the leos need to be around the same weight, unless they get along fine fine without being around the same weight.
And no males together..it could be all females, or one male and 2 females, but obviously breeding would occur, and if the females are two small, they could become egg bound.