Permitted Permutation/Combinations With Some Rules

I have found this very challenging, and have really confused my self on how to systematically approach this. I have the user enter the value in the black highlight boxes, some subtraction produces a base value, the user may also enter the tolerance of the working value (base value), effectivlly giving rise to a small range to generate the permutations from.

What I would like to do then is find all permutations of the inventory (letters in the sheet) with their corresponding values right above them to the small range determined via the user (working value and tolerance). There are also quantity limits for each item. There four basic rules that need to be adhered to:

1) Permutation can't have both S and PP, so one or the other
2) Sum of H and HN must be greater or equal to sum of S and PP
3) H or HN or both must be present, so their sum cannot be zero
4) If HN is less than or equal to 2, and H is greater than 2, then NA and NG must equal 0.