I'm not sure if there are further concerns about the amount of geckos. The biggest issue that kept me from attempting a large enclosure like that was throwing away money on wasted food. You would need quite a few food dishes to ensure your geckos would eat enough.
In a smaller cage you can effectively put in the appropriate amount of food for one or two geckos in one or two places and know that they will get to it.
In a 7 ft enclosure if you only have one or two dishes, some geckos may never even see the food dish if the decide to stay in a particular area, if you divide their food into 7 dishes all spaced equally across the cage, all your geckos may happen to stay in one half of the cage, leaving only half the food eaten and half the amount they need, wasting the rest.
But if your willing to have many dishes and fill them with extra food, knowing some of the dishes will be wasted, it could probably work. You would also want to check on your geckos health to make sure they are finding and getting the proper amount of food each. (If 3 geckos continually converge on a dish that holds only enough food for two and a half for a few days in a row, one gecko could slowly starve)
