Seems like a lot to me. In terms of what is "required" it is 500mg of calcium for Finn's age (actually UK guidelines are lower, only 350mg per day). So 8 ounces of milk is 350mg, 4oz of yogurt is 150mg, and 1 oz of cheddar is 200mg (and cheese especially is very binding). Add in things like oranges, crocolli, sweet potatoes, oatmeal, etc that also have calcium and he is getting a LOT, much more than he needs. Could be a big factor in the constipation.
Don't get me wrong, I know how hard it is and dairy is one of those things that kids will eat - my DS survives many weeks on brotchens, pretzels, crackers, yogurt, cheese, milk and quark
So not trying to tell you to cut Finn's dairy down or that you're giving him too much or anything, just throwing that out as another idea for you.