The guy that owned the Imperial Palace in Las Vegas said that he had 600 cars (roughly) in his Auto Collection on the 5th floor of the casino. He said that 90% of the value was in about 4 of the cars. He only has about 200 on display at a time, the rest are where you can’t see them.
The point is, a collection is whatever you think it is. Lash’s beautiful collection of the wrong brand is a commercial venture like the Imperial Palace. For an individual, a collection can be any size, but if it is all cheap stuff then it is not too impressive. If it is a mix of good and better stuff then it starts to be interesting.
If you have a 3000 square foot basement and 50 rolling stock and 10 locos then it dosen’t sound very big, but if you have 500 boxes stuffed into a 10 x 10 bedroom then you are a big collector, or pack rat as viewed by the CFO. [:D]
A large collection, as has been noted, can be defined any number of ways. If you are collecting something like pre WWI, O gauge , American outline, like new condition, hand painted Marklin, then a “large” collection would be less than 100 items. On the other hand, if you are collecting mint boxed postwar Lionel then large would probably be in the realm of 1000 items or more.
The biggest collections, in terms of number of items, that I’ve ever seen were people who had multiple rooms completely filled with trains. As I mentioned before, one had actually purchased the house next door. Some of the rooms were packed, floor to ceiling with boxed trains with narrow access isles so that you could, in theory, go into the room and find something. Other rooms had trains on floor to ceiling racks which, at least, allowed you to see what had been collected.
Probably the oddest large collection I ever saw was an individual who had collected nothing but factory sealed sets and items. The entire basement of a very large ranch house held floor to ceiling racks of nothing but sealed boxes. The individual had xray pictures of each of the boxes so if you wanted to “view” the collection he would show you the films.