Well, I own guns for home defense, CCW, hunting, hunting out west, shooting with the kids, competition, and for investment.
It is hard to make 1 gun do more than one purpose. For example: CCW. A CCW has to be small, light, and thin, but powerful enough(capacity and power) to be effective against a 1 - 3 assailant situation away from home. This will also require lots of shooting, dropping, wear, holster wear, and just basic use. . .look at a well worn wallet or 3 year old phone which is carried daily. That gun is not going to be a great investment. Nicks, scratches, 1000's of rounds and wear will destroy its value. It doesn't make a great HD gun either because in my PJ's, I need a gun which carries a load of ammo in the clip and a light on the rail.
Funny thing is, OH won't let me hunt with either, so more guns!!!
And at 300 + yards they aren't work a darn, so more guns. . .
Investment: Well, buying certain guns of low to moderate volume and holding them for a few years usually results in some gain. Unlike other purchases, cars, bikes, barbies and everything my wife buys, guns can be turned back into cash(at or near the purchase price) relatively quickly. Everything my wife buys cannot. Shoes?? Used shoes are worth like 10% of retail the day you walk out of the store with them on. Guns, can be worn, shot and practiced with for a year and be sold for like 80-90% of new price! Only a house is a better investment. . .well some house. . .my buddy still owes like $35k on a house he can't live in, but his guns are ALL worth more than he paid for them, so houses are not always a great deal, I guess.
I'll bet my guns increase in value faster than my 401k! WTH! Wish the company would match funds on a gun purchase.
Wish I would have bought that $4500 M16 I saw at a gun show when I was 12. . .My dad and I thought that was soooooo expensive. Now, I think I could turn it for $25,000!
So, I guess my answer is as many as I can afford without taking food from my kids mouths.