I keep my homer's and ferals separated by a long way, couple hundred yard's. Out free flying I have never seen them get together, always in their own group. I suppose you could teach the birds not to land back on the ground as some do, but I found it was a great exercise for finished dog's. As for size, I don't have any homer's as small as the ferals. And the ferals I have a hard time figuring out male from female and been using them over thirty years. I do like them better as they are much easier for me to handle but they don't come back as far as the homer's. Not all that big a deal unless I go somewhere far away to train, I don't! I've got ferals with a lot of white on them, pretty birds. Have one red bar homer that is almost pure white but the bar are there but very faint. I have some that are tri color, really nice birds. The rare color birds I don't fly far, worried a hawk will get them.
The biggest misconception I find is that ferals are no good for homing! Couldn't be farther from the truth, they just don't do it anywhere near as far but, I have had a few I sold, come back 80 miles, the exception! I did have a feral go into the homer loft one time, really obvious the size difference when that happens. I don't know if they will cross breed, never had them together to find out. As for the white birds, I've always heard them called kings, big birds? But not normally a lot of white on any of my homer's, lot on the ferals.