Once I accept a job offer, the salary and benefit negotiation is done? What's the etiquette?

If you feel that there was something that was not covered (wages, benefits, vacation time) give the person a phone call that made the job offer to you. Clarify what the terms of employment are going to be (working hours, job title) and make sure you both have the same understanding. To try and go back now and ask for more money is a bad idea. If you agreed to a specific wage or condition you can't go back now and say "Well, what about this salary?"