Collecting anything is a funny thing to do. Believe me, I know. It's a kind of obsession or can be. But some obsessions are a lot of fun. I'm not sure, however, of the difference between collecting and accumulating. I suppose that if you buy a particular gun for any reason, then buy another a few months later for a different reason, one day you'll open the cabinet and realize you have an accumulation of guns. But it won't be a collector's collection. You can still be as happy as you can be, just the same.
Some gun collecting is stratospherically expensive, like having your Mercedes worked on. Difficult, too. But other varieties of gun collecting can be just as much fun for a lot less money, like owning a Mustang. You just have to be interested in the subject.
I've always found small automatic pistols to be fascinating, which is not to say I've collected them (can't afford a Ford Mustang either). They have been made in incredible varieties in the last 115 years. Some have the added cachet of being used by the Germans in WWII, which appeals to some collectors. I note that some people here have managed to accumulate a nice collection of Model 39 S&W pistols. Cost-wise, that's somewhere in the middle, but you don't see a lot of them in gun shops, do you?
I suppose you become a collector when you want every variety of a certain model that was ever made. Of course, on the other hand, a true gun enthusiast wants to own at least one of every model of every gun ever made, even just for a little while. Even a .22 Sheridan pistol.