Answer: 32

Solution:

There are $\binom{12}{8} = 495$ members of $S$ below $2^{12}$ and $\binom{13}{8} = 1287$ below $2^{13},$ so $N$ has $13$ binary digits, and exactly $1287 - 1000 = 287$ members below $2^{13}$ exceed it. The $\binom{11}{6} = 462$ members whose binary representations begin $11$ are the largest ones, so $N$ begins with $11$ and is the $462 - 287 = 175$th smallest of them.

Among these, $\binom{9}{6} = 84$ begin $1100,$ the next $\binom{8}{5} = 56$ begin $11010,$ and the next $\binom{7}{4} = 35$ begin $110110.$ Since $84 + 56 + 35 = 175,$ the number $N$ is the largest member beginning $110110,$ namely $1101101111000$ in binary.

Its value is $2^{12} + 2^{11} + 2^9 + 2^8$ $+ 2^6 + 2^5 + 2^4 + 2^3 = 7032,$ so the remainder upon division by $1000$ is $32.$