If you follow the link in my signature you'll see why I don't believe in those magic numbers you mentioned or any other magic numbers. You can use those as a rough guideline but you are throwing out some red flags as to why that may not work really well for you.
You say you want more chickens. It is a lot easier to handle that when you initially build. By adding more chickens you will need to integrate. Integration is a lot easier if you have more room than the absolute minimum. Are your bantams going to be chicks? Few places sex bantams so you could easily wind up with several boys. More room might help with that. Or it might not.
I think it is a good idea to have a run where you can leave them locked in the coop/run for days or weeks even if you plan on free ranging. That allows you to have some flexibility in handling issues. There can be many different issues when you free range. Say you host an outside barbecue, you may want to lock them up so your guests aren't walking, sitting, or eating where the chickens have recently pooped. Maybe a predator starts picking off one a day. It might be handy to lock them up safe from the predator while you deal with it. Maybe a hen hides a nest and you want to retrain her to lay in your coop. The list of why you may want them locked in a coop/run is endless. So a run is a great idea.
You don't say where you are so I have no idea about your weather. If you have days where they can't get out into the run shoehorning them into the tiniest place possible can easily lead to behavioral problems. You climate is an important part of this and those magic numbers do not take any of that into account.
For your number of birds, whether bantam or full sized, I'd want a walk-in coop tall enough for me to stand in there and big enough for me to work. You need to be able to access every part of the inside of your coop. That's hard to do after you get to a certain size unless it is a walk-in.
A lot of this isn't about what the chickens need. It's more about you. I find the tighter I pack them the more behavioral problems I have to deal with, the harder I have to work, and the less flexibility I have to deal with issues. I like the flexibility more room gives me most of all. That can greatly reduce my stress and I figure I'm as important as some chickens. The chickens actually benefit too.
