Is my coop/run big enough for 3?

Do you consider that run predator-safe? If you are comfortable leaving that pop door open day and night and you don't have weather where they will be trapped in that coop I don't see any bad space issues as far as behaviors. People tend to think of coop space or run space. Chickens don't. If space is available they don't care where it is. If they are going to be trapped in that little coop for days by snow or something else, yes the coop is too small.

I see you are feeding underneath the coop. Good, you don't have to worry about them pooping in the feed from the roost. I don't see where the waterer is located. You don't want them pooping in that either. If both of those are out of the coop that gives them more clear floor space to land when they come off the roosts. They tend to spread their wings and fly down from the roosts. The higher the roosts the more clear space they need. I don't know where the nests are either. The roosts need to be higher than the nests, you don't want them banging into the nests when flying down either.

I always like more room, it makes life easier for you and helps them too. As long as they have access to the run as well as the coop from a pure space concept they can get by with less. Yours are all pullets the same age so you don't have integration issues. But a really small coop like that just doesn't give you much room to put anything. To me coop layout is the hard part.

I agree with Sourland. It's always good to have a Plan B ready, even if you had more room. You just never know when you will need it.