I'd try swirling the carboy or bucket gently, and increasing the temperature slightly to see if that rouses up the yeast. If not, there's some great info on here about kits getting stuck.
As for the amount of volume versus the yeast, that's a complex subject. Short answer is you would've been fine with 5 1/2 gallons or 5 gallons. The yeast will multiply like little sugar eating bunny rabbits just the same. As you get a few more brews under your belt, you'll want to look at making yeast starters. It takes the smack packs and vials and allows you to create very large and healthy yeast colonies for a quick and healthy fermentation.