A collection of cels = cels owned by a collector.
 :)  And a collector is somebody who is truly
passionate about their hobby, and who, if you
caught them in a corner with their binder, would
be happy to tell you something about each one --
whether that be something about the scene and why
it is special to them, or a fun story about how
they got the cel, or just how much they love the
anime or the character.

It certainly doesn't depend on how many cels you
have, and absolutely not on how much you spent on
them.  (Let me attach a Trigun cel as
evidence -- I love this cel intensely, but it was
so cheap that the shipping from Japan cost more
than the cel itself.  *grin*)  Just the fact that
you're interested enough in your hobby that you've
found a forum to post on is indication enough.

So, since you're a collector by definition, I'd
say your question is moot.  *grin*  Welcome to the
insanity!!