Yep, I think that is a good idea, basically you are looking at eventually putting together a flock of 30 birds. None of what you showed is enough space for all of them to be together. You need something around 8x12 or even better 8x15. Your current style is excellent in ventilation for your climate.
The roosters are a crap shoot, they might work, they might not. Just know that going in, and solve for the peace in the flock. If you can, keep your current set up, always handy to have a second coop (whispers the enabler).
Mrs K