Premade coops almost always over estimate what they can actually hold. You will be OK for a little while, but I would start planning on a bigger coop, or figure how to expand this one. Often the most economical way to get a bigger coop is to convert a used shed. The more run space you have it can somewhat help with a smaller coop. Even if you don't get a larger number of chickens (and most of us get struck with "chicken math" at some point and end up with more than we planned, sometimes a lot more) any time you add or replace birds that's going to make for cramped integration and spats. Deep litter works in covered runs, as said, some moisture is OK, but wet and soggy is not, so heavy rains could leave you with a stinking mess. Basically, if you start smelling stink, then something isn't right. I use deep litter in my covered run, my coop has poop boards so I scrape those daily and clean the coop as necessary. My run can go much longer than the interior of the coop can for cleaning. My covered run is open to the coop, and open to their open, grassed, fenced area during all daylight hours, so they are outside most of the day unless it's pouring rain.
