Well, as far as my actual needs go I would say I "need" five, three of which I already have:
A sporterized Mauser
A Ruger MK II
A Mossberg 500 shotgun
I would like to acquire very soon:
A .22lr rifle
A "real" caliber pistol that is concealable. Probably poly-framed and probably an M&P.
With these five guns I could do just about anything I want to do with guns. I can hunt any animal in NA, and protect myself in and out of my home, plus afford to practice a lot with both rifle and pistol.
Now, as far as wants....
A .30-30 lever action
A .45-70 lever action
A .45c SA revolver
A .357 mag revolver
A .44 may revolver
A mid-range 1911
A nice double-barell shotgun, probably a citori
A magnum rifle, probably a Mauser in an "African" cartridge
Replicas or originals of the 1861 Springfield, Springfield trapdoor, Krag, Springfield 1903, Garand and M1 Carbine.
A stock K98
A PTR91 (G3 copy)
A smith and wesson K-Frame, an old one
That's about as much as I would ever want to have around. This assumes a world were I have unlimited funds and unlimited shooting time. Realistically, I doubt I would ever go over 10. I refuse to not shoot my guns or keep any "safe queens." After I cover my five "essentials" I'll be happy to add an AR15 and after that I'll probably acquire things that really strike my fancy, and probably from the list above.