I am not licensed in CA, but the benefit of an LLC over a partnership generally is that, as its name suggests, it limits liability. If someone eats a bad tomato from your business, and then sues the LLC, only the assets of the LLC will be readily subject to judgment. Conversely, in a partnership, the liability can (and does, generally... Again, I a, not licensed in CA, but doubt it is different there) and does run to the partners themselves. So you could lose your house over that bad tomato...
Why do you want to handle it without a lawyer? You should be able to get a personal injury lawyer willing to take that case on a contingent-fee basis. That means he would collect his fee as a percentage of any amount recovered.
You should find a good employment/discrimination lawyer in your area with experience mediating cases. THEN agree to mediation (if you and your lawyer think that is the best route). You can be sure they will have a lawyer at the mediation.... You should too.
A Corporation must be represented by counsel in a civil proceeding. Because it is a creation of the state, it cannot represent itself (pro se). If a corporation is a defendant in a civil proceeding, and it fires its lawyers, the court will generally give it time to hire new lawyers. If it fails to do so, it could face serious consequences, including a default judgment.
If it was a gift and the title is already in your name, he will have a tough time getting it back. That said, the fact that you quit shortly after, and there appears to be some emotion (on his side, at least) leads me to think that he could argue fraud in the inducement, or something along those lines. You have the title, and that is a great fact in your favor, but this fact pattern has my "spidey sense" tingling.... I suggest you get a lawyer and share the ENTIRE story with him or her....
It sounds like you would not have trouble getting a judgment. Getting your money back, on the other hand..... Well that's another question. You should hire an attorney, give him or her the full story, and that attorney will likely conduct an asset search to see if the purloining plumber has any assets that could be used to satisfy a judgment. Otherwise, this sounds like a case where you would spend a lot of time and effort obtaining a judgment against a judgment-proof defendant.
You write you you were not given any verbal warnings, but you have identified two verbal warnings you received. Your employer may have a grievance procedure that you can avail yourself of, but, based on the facts you have provided, it does not appear that you have a discrimination or retaliation claim.