MOA is an acronym for minute of arc, or 1/60th of one degree. It is very close math that 1 MOA equals 1 inch at 100 yards, but that is just a gift from God that it works out that way.
When calculating long shots with a 1/4 MOA click scope, you are correct in that 1 click will equal about 1 inch at 400 yards, roughly. However, if you crank a regular old scope 30 clicks to compensate 30 inches drop at a given cartridge to hit dead on, you'll be sorry. Most scopes, except for a few exceptions, won't take kindly to that kind of adjustment.
There are sniper scopes that are designed for this.
Really, you might be better off with a good Mil Dot scope, and use a range finder and the dots, FWIW, IMHO.
Hope this helps.