EggWalrus is right about a lower vent that can be sealed off in the cold months ... most vents don't really "seal" ... looks like the OP is planning on using nice vinyl siding ... which would make it harder to just caulk a vent for winter.
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
I prefer hardware cloth doors. I only have a few cold days in winter and I cover them with cardboard, I also have very little wind on ground level so I can get away with it full time. its a good idea to have changeable doors like that provided wind is not an issue in summer, wind driven rain will get inAnd a future (next spring) idea for the OP ... maybe make an additional "summer" door for the end, to be changeable with the "winter door" ... that is basically a screen door, but made out of hardware cloth, that will give you lots of fresh air in the summer, but a closed door for winter.
Small Chick could be a runt, or even a different breed/bantam ... hard to tell when they are not standing side by side ...
See my suggestion on this thread https://www.backyardchickens.com/threads/chicken-runt-question.1278339/
That is one possibility. They could all be roos except the one little pullet. Earlier this year I bought a dozen and every one was a roo except for 3 pullets.The bigger one has quite a bit more comb ... do all the rest have combs like that?
I'm not familiar with RIR's ... but that comb seems big for a less than 3 week old pullet ...
IIRC you got them from a farm supply store, maybe they got some mixed up ... maybe you got a different breed for the little one, or a whole bunch of cockrells
Maybe post your question and pictures in this thread https://www.backyardchickens.com/threads/chicken-breed-focus-rhode-island-red.1021447/page-33