Let's see...
Besides the few dozen crap pipes that I bought as projects for learning restoration, I probably have about 140 pipes, ranging in period from 1882 to 2014. With the exception of a few "museum pieces" I smoke all of them at one time or another. The largest group are the Barlings, hovering in the upper 80's. While I enjoy looking at pipes, I'm pretty much done buying them.
If one's only concern is for a Nic deliver system, one pipe is enough. Above that it's wasteful effeminate extravagance.
If one has a brain that functions on a more complex level, the numbers start to rise.
I like a wide variety of blends so I don't smoke English/Balkan blends in the same pipes that I use for Va/Pers. I like to taste what I'm smoking as opposed to what I had yesterday or last week.
Nic content is not important to me. It's about flavors, so I've cellared a variety of blends that I like, and have experimented to match blends to chamber shapes and sizes. Not all blends deliver equally well in all pipes. A range of sizes and shapes helps deliver the flavors in the blends I like to smoke.
Besides flavors, I'm interested in the history of pipes and tobaccos, the esthetics of pipe design, and the shapes and styles of pipes from the early 20th century as well as a few contemporary artisan makers. These interests also raise the body count.
There are a lot of ways to enjoy pipes and tobacco, ranging from a couple much used and loved pipes and blends, to enormous far ranging carefully curated collections of rare pipes and rarer tobaccos and tobacciana, all of which may just be for visual display and not for actual use. And there are all sorts of points in between. It's all good.