Apparently the average self-published book sells 200 copies during its lifetime. The average traditionally published book sells 1000. Of course we authors try to do better than that if we can. In Canada a book that sells 5000 copies is often deemed a bestseller. In the United States the number is several times that.
Regarding printing: Digital printing [using high-powered laser or inkjet printers] is generally appropriate for books with a print run of fewer than 3000. For those with a print run of 3000 or more, offset printing is generally the technology of choice.