Winterizing, is my coop/run big enough?

[AnnPann]

Also, keep in mind the calculation for "how many can fit" is not "existing chickens + new chickens." Let's say you have a coop that fits 8 chickens. That is good for 8 chickens that like each other/get along. Adding 4 new chickens chickens to an existing flock of 4 chickens means you need space for more than 8. I learned this the hard way.

 

[aart]

Is there any world in which my existing coop could be modified to be comfortable for 7 hens by using a couple of the nesting boxes as extra floor space (there are currently 6 boxes, that seems excessive, I can easily remove a divider or two) and mounting the 3 floor roosts so they're above the diagonal roost? What modifications should I consider if I'm planning to add 4 more birds to the flock or should I just plan to add a second coop to accommodate them that opens on the run, extend the run, and let them decide which hen house they want to sleep in for the night?

No.
Integrating more birds take extra space.
A coop large enough for the number of birds you want would be the best way to go.
A second coop would get you to having 2 flocks, because they' all want to be in the same coop eventually.

Get thru this winter with the 3 you have, it's going to be tough as it is.
adding more birds to the mix spells disaster(or at least misery for both birds and keepers).