We could have a long discussion about how much is enough. That discussion has been had here before . Also Peter shared his thoughts. Of course the scenario(s) you are preparing for matter considerably here. I listed my chosen amounts. That is for a pretty nasty situation but maybe not quite a full on mad max one. Half of that, or even a third, is plenty for some sort of short to moderate (say a month or two) type event like Hurricane Katrina or whatnot.
The point is that you need to get whatever you feel you need sooner instead of later. Also it is not a bad idea to think of some overages for family/ friends/ neighbors. Case in point I have a stash sufficient to let me give a neighbor 50 rounds of 9mm or 50 rounds of .38 special , ditto for a few mags of 5.56 or 7.62x39. Still I could stand to stash some ammo specifically for this eventuality. Say some buckshot, about 250 rounds, since my neighbors all seem to be into the duck hunting and thus shotguns. Also if going full bore I'd stash 100 rounds each of .40 S&W and .45 since I have little (.45) to none (.40) of those common calibers on inventory. The point I am getting at is that you should plan for whatever ammo you might give out in an emergency above your personal stash.