Can you give an example? Not sure how big of a difference you mean. Like there's a pretty big difference between people of some different asian countries. Or people can be from different countries, but still be very close. Really depends on the specific situation.
Can you be more specific?
Are we talking like a white guy, who looks totally white but has a low percentage of asian for example? Or more of a 50/50 ratio?
You mean like Arabs with Arabs or Indians with Indians? This is totally fine and natural. These sub races are their own race now. But as far as I know go for the one that looks more like you. The reason I say this is because you have light skin Arabs and Indians and I think it was written that it's best for the light to go with light and dark with dark, in accordance to each race. I think this goes for dark Asians and light Asians as well. If I'm wrong hopefully someone can correct me on this.
I think you mean different ethnic groups or different nationalities because you can't be the same race and different sub-races at the same time. Indians, Mexicans, Native Americans, Arabs, etc. are all sub-races.
But if asked me it would be nice to see redheads with other redheads since those specific whites are the least amount among whites from what I read. Who wouldn't want to see more families of firey redheads running around but I digress.