I would like to know, from someone who has marketed a collection of short stories (or is otherwise knowledgeable in these affairs), about how many short stories a publisher is looking for to constitute a collection. Let's assume all the short stories are between two and ten pages long.
Short story collections are notoriously had to place over the transom. Typically a writer will have published most or all of the stories in other venues and then work with an agent to market the collection...at which point the length will vary widely depending on the publisher.
At any rate, there's really no rule of thumb due to the differences between publishers. Do you have publishers in mind? Have you published any of the stories in publications that are likely to be of interest to a publisher?