I signed an agreement to release all my interest in a Family Trust which I now deeply regret.

This agreement was made in consideration of a sum of money, was notorized, states that I was of sound mind, and on the surface appears to include the basic elements of contract law. However, it was not drafted by an attorney and may still lack proper legal form. Also there was a lack of true disclosure of the facts upon which the agreement was made. I feel there is enough reason to have a court look at the agreement and decide if it should be considered legal and binding.

Can I sue now to have a court rule that this agreement is in fact invalid, so that it would not be allowed consideration by future courts should I need to sue the estate for my rights and benfefits as a beneficiary? If so, what level of court would be appropriate to make that ruling?

A contract doesn't have to be drawn up by an attorney to be considered valid. As long as the provisions of the contract are clear and they have all been met, then the contract is valid. Your best hope of overturning the contract is the disclosure issue. If one party of the contract did not disclose material facts that might have affected the other party's signing the contract, you might be able to void it. I would take the contract to an attorney and ask their opinion.

I am sure you can always find an attorney who you can pay to sue for anything.

A contract to be binding has to only meet the specific state law in the US in which it was signed or at times had legal bearing.

Some contracts don't even have to be in writing, as long as it can be proved.

So you can try, it would mean you would have course have to pay back all of the consideration ( payment) that you received also.

But it is a maybe, if you can win, depending on the terms of the trust, and the wording of the agreement, plus as noted if there was any fraud or misrepresentation of the agreement

Did you receive your end of the bargain, i.e. the "sum of money?" If so, then I doubt that you'll have a leg to stand on as remorse after the fact would generally not be considered grounds for revoking a contract. Would you be prepared to give back the money you received in return?