Most states call for 100 amps minimum, but with all the new electronic devices, air conditioning and electric heat, I would suggest 200 amps especially in new homes. This also gives you some space for future additions. This is not a job for an unlicensed person to attempt. In most cases it involves replacing everything from the service loop (this is the wire that extends from the top of your meter to the utility tie in ) up to and including the main panel.