Depends what you want to do, you don't have to be online at all for the PS3 to work.
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First you need the master account and then you can follow instructions on related link The links are from Playstation support USA and also cover every PS3 screen that you need to have completed for creating the master account and there is also a separate link for creating the sub account
you go to the ps3 account station and they will give you the password to your new account. sukka
At the settings menu for the PS3. PSN settings are set in the master account after you are connected and logged into the account
buy a new ps3
Yes, you can.