Portagegirl did a pretty good job of explaining my thinking. This might help you understand better but I warn you, Henks calculator can become addictive.
Cross Calculator
http://kippenjungle.nl/Overzicht.htm#kipcalculator
When you get to this link, go to the second choice above the rooster which is the English version and click to make a selection. You can choose anything, but try red. Then choose something different for the hen, say black. Then, to the right, select To chicken calculator. A new screen will open. Go to the bottom where it says calculate crossing and select that. You will get a black male and a black female to come up. Choose Continue with this female and Continue with this male, then again select Calculate Crossing. Now scroll way down and you can see the options of what you might get. This is just with basic black and red.
Try it with a few selections of your choosing that include other things that control pattern instead of just color, say red mottled x Columbian. Or cross the offspring of two totally different crosses. If you do a bit of this, I think you will understand a lot better.
It is possible to select hens and roosters so you will always be able to tell which chicks came from which pairing, but it does limit you some. Say you have your BAs hens and get Buff Orpington hens and roosters. Any black chicks will be crosses but any yellow chicks will be Buff Orpingtons. But if you choose BA hens and roosters and Buff Orp hens, all chicks will be black so you will not know which chicks are crosses.
One full sized rooster will normally keep at least 10 to 12 hens fertile. More hens than that per rooster and the fertility can drop off. It is quite possible that one rooster can keep 20 hens fertile. It depends on how active and such he is, but two roosters with 20 to 25 hens assures they will practically all be fertile. If both roosters are the same breed, then you will be sure of that sides paternity.
You have mentioned a few times that you may want to sell chicks, thus you want to have one pure breed to sell. There are pure breeds and there are pure breeds. Certain breeders try very hard to come up with show quality chickens that conform very closely to the standards for that breed. It is not easy, requires a good understanding of chicken genetics, requires hatching out a lot of chicks and carefully selecting only the very best, very good record keeping, and is not cheap. Others keep a pure breed, but they dont go to that much trouble to maintain or select to the standards. There is a tremendous difference in the appearance of a chicken bred to standard and a purebred chicken. It is body conformation, color, patterns, shape of comb, color of legs, many different things. If you breed chickens that regularly take championships at the shows you can get a lot more for the eggs and chicks. If you dont breed championship chickens you need to advertise them as not show quality. Pure breeds not show quality may be easier to sell, but if they are going to be pets or egg producers, it really doesnt matter if they are pure breeds or crosses, also known on this site as mutts. If you cross Orpingtons of different colors, you are certainly not going to have show quality chickens and they will not conform to the standard Orpington colors.
It comes down to what you really want to do and you obviously have to ask a lot of questions to make a good decision. Hope Ive helped a bit.