From a self defense standpoint since handguns are worthless except as a backup, probably none!
However since rifles and shotguns are hard to conceal from a self defense standpoint and carrying concealed, AT LEASE one concealed carry handgun of your choice.
From a hunting standpoint, if you hunt with handguns, depending on what you hunt a couple of handguns to maybe a half a dozen.
I have a few handguns and I like to try out new and old and different handguns so my safe kind of has a revolving door on it. The old classics that I like, I keep, the new handguns that I like, I keep, the new or old handguns that I try and don't like, I sell. For example, I sold a long time ago a Seecamp 32 auto, in the not so long ago past a Kahr PM40, and just recently a Kel Tec PF9. I also sold a Glock 27 and a Glock 36 which were great handguns I just needed to pare down my collection a little. Handguns I would like to buy and try in the future are CZ85 Combat, Dan Wesson Valor 1911, Caracal 9mm with short sights, Colt Python, Walther TPH, Smith and Wesson model 41, Freedom Arms 454, etc etc just to name a few. Do I need any of those handguns, nope!
Actually I have given some serious thought to selling almost all my handguns and investing in rifles and rifle ammo, AR's, AK's, 308 battle rifles, long range rifles and hunting rifles, as I don't want Switzerland to get ahead of us in the arms race!