Looks like a great start! Love the paint job! Congrats.
Your nest box location looks great, easy access from the gate and if you cut a hole and hinge it, you can see in before you collect too. I've read too many "snake in the nest" stories! Remember to have the roost higher than the nests for cleaner nests and you may want to make a "ladder" to the roost for young birds to learn on. Be sure the roost is not too high up to avoid injuries but big and strong enough to support all the birds at once (I use 1 1/2 inch tree branches or saplings)
A poop shelf catches a large amount of the poo mess (I believe about 75% since they poo a lot in their sleep) and having easily removable metal or plastic pan(s) expedites cleaning. Maybe even mount then on drawer tracks that roll it out thru the wall for cleaning access.
As to number of birds, use the guide of 4 sq ft in the coop and 10 sq foot in the run, per bird. Go with the smaller number of the 2 numbers for happier birds and could probably go with more birds if you run bantys. Elevating the coop lets them use that run space too, plus it's more shade.
I run coarse sand in my main coops as litter because I'm cheap and feel it's easier. With chips or straw, you have to completely remove the litter to be clean and dry and you may have a disposal issue, unless you compost, you may have to haul a large trash can if caca to the dump. To clean sand you can simply rake and scoop with a kitty litter scoop and it does not absorb moisture unless trapped by your floor by a major spill . Sand also provides grit and a dust bath area for the birds.
Remember to skirt the fence and if you can, a strong wire top will add to Ft Knox type security plus the birds can come out as early as they wish, letting you sleep in sometimes.
Don't be afraid to cut some big holes and wire them for ventilation. A old single pane window does great too plus it allows closure for bad weather. Just cut the hole a little smaller than the frame, cover with wire, attach the window frame to the wall with hinges at the bottom and a latch on top, add a chain or string to keep it from falling too far open and you're set. It get hot and you can pop it open for more air but even closed it gives you light to see by.