Hi, Lisa. Welcome to the forum, glad you joined.
I think you'll find most of this personal preference. We all have our opinions and experiences, many of them quite different.
In Arkansas my 8' x 12' coop had one standard sized window I salvaged from a house upgrade on the north side. I can see well enough in there on a cloudy winter day to do anything I need to. The chickens have not complained, they have not sent me any petitions asking for more light or gone an any strikes wanting more light. I also have a lot of ventilation up high which lets in a lot of light so that might factor in. I don't know what the rest of your coop looks like.
I don't know if you have security lights that might shine in your window at night. They need a certain amount of dark downtime. In my coop the section of the roosts next to the window is prime real estate for roosting. If you have a bright light just outside they may like that or they may not. But I'd try to keep the roosts from being too bright at night. In winter you don't want a cold breeze blowing on them but in summer a breeze is nice. There is nothing wrong with having a window that can be closed in winter and open in summer at any height. Just install hardware cloth for predator protection when it is open.
You are in Maine. That's good information. Your location often is, thanks for mentioning it. Putting your general location in your profile makes that information always available.
You will probably get some pretty warm days in the summer but nothing like others deal with. Of course what your coop looks like, how it is shaded, and how the nests are made can make a big difference, but I try to avoid nests on walls that will heat up in the sun. For you that is probably south and west walls. I don't want the nests to turn into ovens. Nests hanging external or closed type boxes inside would be more of a concern than a nest inside that is well ventilated. This is probably not that big of an issue for you but maybe something to think about. I don't worry which side the roosts are on from a heat perspective. They use roosts at night after it has cooled off.
To me the main thing is to make the layout convenient to you. The chickens really don't care that much. They really can adapt to many different things. The more comfortable you are working in there the better care you will take of the chickens. Always think of yourself, that's not being selfish.
My personal preference is that the nests not be real bright. I don't know that this is better, it's just my preference. I grew up on a farm where the chickens free ranged and several hid nests instead of laying in the hen house. Those hidden nests were generally in darker well shaded areas. That does not mean they won't lay in brighter areas. In my coop most of my nests are fairly dark boxes with just an opening in front for the chickens to come and go, but I once used a cat litter bucket totally open. They used them all.
I don't think there is a "best" arrangement. Making it convenient to you is, to me, the most important.
I have 5 in a 6x10. 
