During warm months and good weather the garage door is open on the shed, so I will only have to worry about these winter months with the lack of sun. I didn't have the pens in the back this spring/summer/fall, so the birds in the cages got plenty of light. I still have 3 windows to put in the south facing side of the shed. I didn't get there before it got cold.
The birds in my cages have nearly 12sq feet. I like to stick with a 2sq ft per bantam rule and a 4 sq ft for LFs. The cages are only about 22" high, so I would never put a LF bird (I have Ameraucanas - small LFs!) in them unless I absolutely had to (injury, sick, conditioning, ect.). A trio of LF should have at least 12sq foot and bantams should have at least 6sq foot. I really like to have an extra bird or two's worth of square footage, though.
I haven't had any issues with breeding in the cages - no more than normal with the Cochins since I have to pluck their butts.