On a scale of 1-10, If one can prove an issue of a radical jurisdictional defect, what are the chances of one getting free?

You will need to give more facts. I agree with the other answers already posted.

Yes. Pleading guilty counts as a conviction.

Can I as a cosigner sue the primary borrower.

Yes. You can bring a third-party complaint for indemnity and contribution. Hire or at least consult with an attorney-this is a bit tricky.