Sounds like a great success. Back when (long before ebooks) I helped with their self publishing. A minimum press run of the book-length projects would often be

Sounds like a great success. Back when (long before ebooks) I helped with their self publishing. A minimum press run of the book-length projects would often be 500 or 1,000 copies. I'd tell authors to expect to sell half the run or less and to be generous with "review copies" and so on.