One can always add chickens, after the coop is built. I did not mean for the original poster to only have 2 chickens forever, but it better to add chickens after the coop is built rather than adding chickens now and building in the spring.
So I think adding a single chicken now, then build a...
Just get one chicken. You coop is small, and it will be very tight for 3 birds, two of them strangers to the home girl.
One on one, there will be a dust up or two, but it will quickly settle. I would add some clutter to your run, you are wasting all that vertical space for the birds. And a hide...