I know this is a little late but...
Mix all the breeds you want, I've never met a bigoted chicken :lol2:
I like the redstar/red sex link for high production brown, although I'm very fond of Rhode Island reds also. They're very calm and still have outstanding production. Leghorns are my choice for high production white eggs, though I prefer the Lt brown, Red and Exchequer varieties over the White. They're a highstrung breed in general, but the whites seem to be the most so in my experience. I have Americauna's for green/blue eggs. I have Welsummers for the dark brown eggs. They're half the price of Maran's, and more readily available. I have numerous other breeds in white and brown layers that are just attractive birds, or are very calm birds but don't lay quite as prodigiously.
I do give them garden and table scraps, but still feed a full ration of commercial feed for max nutrition. I use a 24% game bird feed mixed with corn chop so that I still get a 16% feed. Oyster shell is available free choice. And I also feed alfalfa bales because I can't free range here due to predators.
3-5 birds, depending on breed and how many eggs you eat, would be plenty for you and your family. If you eat eggs everyday, bump that up a couple.
I second that you may want to get a couple of 6 month old pullets to get started. You'll have eggs right away (put a light on them this time of year). Chicks are really cute for about a week, but getting the eggs seems to hold a kids interest a lot longer. You can still get chicks in the spring when it brooding is easier. And then add them in with your other birds when they're old enough.
Your 10x10 pen is a big enough yard for 4-5 birds max. You may still want a small coop for nighttime and nest boxes.