I take a somewhat different tact that most. I stick with the big name retailers like Cabela's, Sportsman Guide, Midway USA, etc. I pick exactly what I'm looking for (Hornady TAP, Winchester White Box, milspec 5.56, whatever) and backorder it in as large an order as I can afford. Then I wait patiently in line for the backorder to be filled. Midway will let you ask to be alerted by email when particular items come in stock and have estimates of when they expect it.
That seems to work better for me and is much less stressful for me than hitting stores weekly and coming away empty handed or buying whatever they happen to have. It also beats sacrificing half a day to attend a gun show having grubby people who seem like they haven't bathed or shaved since they were last employed, and paying money for gas, parking, and entry just for the chance to buy reloads of unknown quality. I just punch a few buttons on the computer and open the package when it gets here eventually. I've ordered perhaps 1,200 rounds of various .223/5.56 and about as many rounds of 9mm in the past few months. Both in calibers and brands that were impossible to find locally and exactly what I wanted.
As far as how much to get. I tend to try to keep on hand a few hundred rounds of serious defensive ammo for my main guns (Hornady TAP, Speer Gold Dots, etc) after running a couple of hundred to check for accuracy, reliability, etc. Then I try to keep 2 or 3 months of range ammo on hand reordering a couple of months worth when needed. I don't really anticipate needing several thousand rounds for anything. At the end of firing a couple of thousand rounds in anger, the chances of me being around at the end of it are fairly slim. If I do beat the odds, there should be lots of weapons and ammo to pick up.
