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If someone in your situation creates a corporation or a corporate entity, then it is recommended to apply for an EIN. If someone in your situation chooses not to have a corporation/corporate entity, then an EIN is not required.
If a corporation or a corporate entity is created, then it is recommended to be an LLC. An LLC provides the liability protection of a corporation but also allows for ease of running the company by less paperwork requirements and looser rules for conducting business, etc.
It is your decision where the LLC (or whatever you file, if anything) would be located. It does not have to be in PA or NJ, and can be in a state which gives favorable privacy/tax status to corporations such as Delaware. However for practical purposes, it is best to have the LLC based out of the office, so this would be PA if one's home is in PA.
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