I would go with a coop about 8x8 for 10 chicks... especially if you get any kind of winter. Snow and blowing wind might make them reluctant to venture outside, or stay outside for long... so way more inside space is needed.
Also, a roofed run to keep snow out is excellent. If there is no snow in the run, and if you wall 2 sides of the run to block wind, they will be MUCH more likely to enjoy time outside. So... less crowding... less bad behavior.
And yes, electric to the coop for dark winter days and a heated waterer would be great.
I like stacking my coop "stuff" to maximize space...
So under the poop shelf put nest boxes. I love poop shelves.
Or, I really like the removable wire front that fits under 1 of my poop shelves and makes that area perfect for raising chicks, or putting a broody... or whatever.