I'm new to chickens so don't have the experience to give feedback, but just wanted to comment on how adorable your plans are! Also, stoked to see another urban chicken-keeper here (I'm in Oakland, CA). I'm building an 8 x 10 coop for my four girls right now and it's taking up almost half of my yard, so chicken math can't get too out of hand. Elevating the henhouse to at least two feet to give them usable space underneath is one consideration you may want to make?
Apologies but I can't resist...what is that, a coop for ants?