don't count on work. you may be able to swing something but the nz govt have been known to do inspections, especially in hotspots like queenstown. most employers don't want to run the risk of getting busted. that being said i did know people who were working under the table. won't hurt to ask around when you get there.
as far as id goes, i was 25 while i was there and got carded EVERYWHERE, and they would only accept my passport.