Hi! 
Welcome to BYC! You are so smart to build your coop before getting your chickens. 
The size will dictate the amount of chickens will work out for you. One rule of thumb is 4' per chicken in the coop and 10' per chicken in the run. I find that to be too small for my flock, but it has worked for others.
As for the rooster, unless you are going to get a full grown (1 year) rooster and go through the integration process, which takes quarantine and then slow intro, I would wait on the idea.
Even when they grow up with your pullets they go through a hormonal stage that is hard to manage, but then sometimes isn't. Each bird is different. 
It just adds another level of complication when you are learning about chickens. I would go pullets only this year and think about adding a cockerel or rooster next year. 
Welcome to BYC! You are so smart to build your coop before getting your chickens. The size will dictate the amount of chickens will work out for you. One rule of thumb is 4' per chicken in the coop and 10' per chicken in the run. I find that to be too small for my flock, but it has worked for others. As for the rooster, unless you are going to get a full grown (1 year) rooster and go through the integration process, which takes quarantine and then slow intro, I would wait on the idea.
Even when they grow up with your pullets they go through a hormonal stage that is hard to manage, but then sometimes isn't. Each bird is different. It just adds another level of complication when you are learning about chickens. I would go pullets only this year and think about adding a cockerel or rooster next year. 
I’d suggest four or five girls, and a rooster. Roosters give the hens a leader, a protector, and a general sense of security. Not to mention fertilized eggs for hatching fluffy little babies! 
