Volenti non fit injuria is a defense to a tort action (at common law) not a contract action. No one can predict if the Plaintiff will win. Attorney fees can only be awarded if provided in the contract or by statute. Legal interest in California is 10% p.a. from date of breach. Practical advice - if you use latin in court, you will be the object of jokes.
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Volenti non fit injuria is a not a viable affirmative defense in a breach of contract or collection action.
No one can predict the outcome of your litigation, even if provided with all of the facts.
Yes, prejudgment interest can be added to the principal amount in a judgment.
Yes, if the contract or a statute provides for attorney's fees, the prevailing party will also be awarded reasonable attorney's fees.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult with your own attorney.