Same age cockerels tend to be a problem. But while I understand you want to do things right, there really is no predicting how multiple roosters will act. It tends to work until it doesn't, and it can be a wreck fairly fast. The best rooster ratio, is the least amount possible. Often times people have the misconception that if they are raised together, they will be life long friends, and that is NOT the case in chickens. Being raised together has almost no influence on chicken behavior.
If you are getting all those different types of chickens, I would not get the polish roosters at all. There are people (generally people with a large amount of room and a great deal of experience) that can run standard and bantam size birds together, but I have also seen respected posters who say, they went to two separate flocks, because it never seemed to work well.
If you are new to the chicken game keep it as simple as possible. The best would to just get hens. A lot of people just order hens and wind up with a whoops rooster. I would plan to keep just a hen flock for a year, and add a nice year old rooster next year. Good roosters are easy to find and cheap.
If you decide to raise up the cockerels with your pullets, it is best to have a way to pull out the males until the pullets are laying. Cockerels mature earlier than pullets and can be very hard on them. The more males you have the bigger the problem.
Also - free ranging out in the yard, does not make up for too small of space. 18-20 birds are going to need a building size coop ~ 80 square feet, so an 8x10. and a run at least 200 square feet. Overcrowding birds leads to ugly behaviors.
Another question, which is hard, can you cull a cockerel that becomes aggressive with the pullets, or with each other or with humans? All three of these outcomes are real possibilities.
Mrs K