The location of your door(s), window(s), pop door, and vents are the controlling factors. If your door swings in or out may have an impact. The number of total chickens could be important. Diferent people put different things in the coop. The basics are roosts and nest boxes, but many people feed and water in the coop, some build in brooders, dropping boards, or some place to isolate a broody. There is not really a fixed set standard of what goes in a coop.
I'd start with the roosts. How many do you need? I try positioning them away from traffic areas and the doors. In front of a window is fine but not required. Put them where the chickens will not be sleeping in a draft from your wintertime ventilation. I'd suggest that they be about a foot higher than the top of your nest boxes, but the actual height and installation can wait until your nest boxes are in place. Right now just decide how many and where. When laying out the inside of the coop, try to keep the area in front of the roosts free. Chickens need a clear landing area in front of the roosts.
Then I'd place the nest boxes. I suggest a minimum or two, even with just three hens, but generally put one nest box for every four hens. Six hens means two nests. Ten hens means three. Try to position them where the light from the window does not shine directly into them, though that is not really that critical. Chickens generally look for a darker, secure, hidden place to lay so they can hide from predators, but the light shines directly into mine and they work OK. That "dark" is a nice to have, not a requirement.
Some people build their nest boxes under the roosts and use the top as a droppings board, but that can be inconvenient when bending over to gather eggs. Think what your head could bump into. I put mine on the side wall about 3 feet in front of the roost. That way the chickens can use the top of the nests as an intermediate step when getting to the roosts. That intermediate step is probably not required but mine do use it a lot. Some fly straight to the roosts from the floor though.
That is all you really need inside a coop. If you put anything else, just try to position it where they have a clear space to come down from the roosts.
I just saw your photo. Looks like it is in a pretty area. I can't tell how much ventilation you have. You probably need quite a bit in the summer due to the heat, but you also need a lot in the winter to get rid of moisture.