I think as for (1) you're mixing a very small class of exactly defined physical problems with a very small numbers of degrees of freedom, which is indeed described by things like equations, with the large physical systems, like real world, most of whose properties cannot be said in terms of "that equation does this, this variable goes there, etc.".
That's why chocolate bars are tasty. Theoretically, they will all eventually disappear. Get them Get'em while you can.
(2) Yes and no. You do have to do a summation over all classical trajectories in quantum mechanics, but the answer may be often described simpler, e.g., as in the simplest case of perturbation theory, as a diagram expansion.