A model release is not required by law, but it is a contract between two parties (producer and model) about compensation for the royalties earned off the material. So that is completely upto you, I would have some sort of contract in this day and age never know when (heaven forbid) a divorce might happen.
As for the address, not sure about "private parties" but on our business filings you should have a business address that should satisfy the requirements for a valid address since it is a business.
This is not advice just opinion below, please consult your lawyer:
The context of the law regarding "valid address" is written with the intent to make sure prompt response and a entity be it a business or person can be held criminally/civilly liable for the infraction of this law. I would assue if you used a mail drop (Mail Box etc..) since they are required to have a copy of I.D. and SSN on file (postal regulations) that you should be okay providing you answer the requests from the D.O.J. in a timely manner. If you answer a request and the D.O.J. wants to prosecute because of your choice of address doubt you will get a judge to convict you due to the fact you used a mail drop, but if you ignore the requests and they have to come looking for you it doesn't look good might show an intent to evade your liability.
