If you have the space and facility's do 50 at a time.....
This assumes you have a brooder and some sort of coop. I raise a lot of chicken, 150 at a time starting in the spring and ending in the fall, I get birds every 3 weeks. They are raised in chicken tractors and the taste of these birds is incredible, the best chicken you'll ever eat incredible. Here's why I say atleast 50:
When ordering 50 you can get them for about .90 shipped each
With a family like yours you'll prolly going to eat a minimum of 4 birds a week, but prolly more.
Just because you start with 50 doesn't mean you'll end with 50, figure on 10% loss of its less than that great.
Once you process the birds you'll have enough to have chicken at your leisure, if you did 25 and you lost 5 you would run out of chicken before the next batch is ready. I've learned the hard way you don't want to have to ration yourself simply because you didn't get enough birds.
Ok so now that we have a base line, 50 birds will eat around 800lbs of feed in 7 weeks. That equates to about $5 a bird out of pocket before processing, you absolutely cannot buy food that good for that price. We have our birds processed because of state limits for about $3 each. That's $8 per bird.
If you have additional questions let me know, I'll try to answer them the best I can