I agree with the double doors. Hubby built our coop, the access doors to the nest area are large double doors. I have plenty of room to reach in to clean. They don't go all the way down to ground but they are large, opening up the nest box nicely. I can lean in and reach corners. You have a nice coop great job.
I'm a newbie to chicken keeping but, from what I gather...
The Purina coop plan says 8... But if you have enough perch space (I have 4 perches in mine) AND good ventilation/air circulation, I think you can go up to 12 without problems... That's what I intend to do... Given that they're only inside the coop to perch during the night and that you need an average of 1 nest per 4 birds (3 nests in the Purina coop plan, 3 X 4 = 12).
Like I said, this is just my educated guess... People with chicken raising experience (not me!), may tell you otherwise.