I know many people who own many guns. The greatest characteristic that links them all is the fact that very few of them ever own two guns that are the same. They simply had to buy the latest and greatest handgun, meaning they might have a commemorative Colt 1911, a .45 XD-M, a FN-FiveSeven, a .40 SIG, and a 9mm Kahr. NONE of these guns take the same magazines, most use different ammunition, and all of them work differently. While no doubt this arsenal would be a blast to shoot at the range, it has several disadvantages. Standardization should be the primary goal of building up a collection of guns. There are innumerable arguments for and against various calibers and actions.
My advice would be to find the style of gun that is most comfortable for you and then stick with it. One should ideally base your arsenal around a full sized gun such as the Glock or 1911. Full sized pistols are far easier to shoot, are more reliable, and if/when a major collapse occurs, you won't be worrying about concealment. If you wish, you can then buy the "mini" versions of your full sized pistol, like the baby Glocks or the little 3" 1911s. Assuming you based your handguns on the 9mm Glock, you would be able to use the full-size Glock 17 as a home-defense/apocalypse gun, and carry a Glock 26 on a daily basis. They both take the same magazines and ammo, and use the same parts.
This same idea applies to long guns. Owning an M1 Garand, a Bushmaster M4C15, and a H&K 91 is not a good idea. Although each of these guns is an excellent gun that would serve its purpose well, the wide variety makes it difficult to stock ammo and magazines. I have often heard the excuse that it is best to have a wide range, as it will make obtaining ammo and parts post-collapse easier. I have acctually heard this used to justify the buying of a .50AE Desert Eagle! "You never know if you might find some ammo for it!" This veiw assumes that there will be means of obtaining/finding ammunition or parts post-TEOTWAWKI. I believe that it is better not to count on that, but to rather stock up on the ammo and parts for your guns now, so you KNOW that you will have what you need to keep them running.
Keep your powder dry!
