As to "1000's"--

Dave's point is probably technically correct, but I'd have to believe that "1000's" is pretty well understood by most to mean "thousands."

Given that it will be used that way, I would say the apostrophe is correct for the plural. "1000," like "TV" or "ATM," is not a full word, and would qualify for an apostrophe-s to form the plural, as in "twenty TV's," etc.