So, you're only going to bring the exact number of rounds?
Figure 5 mags per stage as the max, I know some will be less, some more.
Figure 10 rounds of rifle per stage, again some will be less.
Figure 6 rounds of shotgun per stage, yes again some may be less.
Then you get 350, 100, 60. And that's with no reshoots.
Yes, you might go home with some unspent rounds but why should that matter, at least you've got enough to shoot the main match.
As for side matches, figure out how many times you want to shoot speed this or that and do the match.
It's not rocket surgery.