Who told you that? 1 with 77 zeroes behind it is just 1, doesn't matter how many 0 you add behind it, the total number of keys is called N, go search for it, it is also the private key for the end range key -1.
What are you talking about? 100 is greater than 10, and 1000 is greater than 100. Obviously, the number of zeros behind the 1 matters.
Bitcoin has approx this many possible private keys:
100000000000000000000000000000000000000000000000000000000000000000000000000000
Whatever that number is called. A private key is a 32 byte array, and that above number is how many possible combinations a 32 byte array has. It's basic math.
Well I don't know what byte array stuff are, but the exact number of bitcoin private keys is FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364140 or in decimal 115792089237316195423570985008687907852837564279074904382605163141518161494336.
What you described earlier, a 1 with zeroes behind it looks like this 000000000000000000000000000000000000000000000000000000000000000000000000000001 maybe "behind" means something different in your world, like front? Tell me, are you from the upside down world? Lol.
Number you posted above is this in hex : dd15fe86affad91249ef0eb713f39ebeaa987b6e6fd2a0000000000000000000 and that doesn't look like N to me. Maybe try to be exact next time, maybe you meant this ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff which is 2^256 -1, so if we add 1 to it, we'll have 10000000000000000000000000000000000000000000000000000000000000000 in hexadecimal = 2^256 exactly.
As I said, we are from different worlds, but please try to provide correct information.