He can file N-400 in June 2005 (90 days before 5-year GC anniversary), and natualization takes normally 6 months to 2 years. And you need additional 3 months to get EAD after you file I-485 (after he granted citizenship) if you want to keep working legally.
It is likely that the EAD will come after July 2006.
It is likely that the EAD will come after July 2006.