We will increase coop size to 6x3 today but right now it is much smaller. The roosting bars will be 2 bars 5 ft long. Ventilation is poor but once we have cut the door open and enclosed the run we will have additional windows added. Climate in southern Indiana cold-mild winters and hot summers. Wet in the spring.
The new dimensions should work for your 4.Ventilation is always key. 1 sq.ft. of ventilation per chicken is a good rule of thumb. The ventilation will need to be as high up as possible above the roost bars so they are not in a draft situation in the winter. What are you doing for nest boxes?