Stuffy Doll blocking 11/11 trampler. Phyrexian Obliterator blocks 11/11 trampler
You should have only taken 1 damage.  When damage happens, you choose how to assign your 11 damage. You must assign at least 1 to Stuffy Doll. Because your creature has trample, you can assign the other 10 to your opponent. Even though Stuffy Doll has indestructible, 1 damage is still considered lethal damage. So Stuffy Doll will take 1 damage, your opponent will take 10, and Stuffy Doll will deal you 1 damage. 

Similar thing for your other question. Your opponent must assign at least 5 damage to your obliterator. He can assign as much as 11. So how many permanents he sacrifices depends on how much he chooses to assign. If his creature does not have trample, he must assign all 11 to the obliterator, and he will sacrifice 11 permanents.