I agree with my colleague. Practically, though, if you do not know the benefits or nuances of having LLC, most people are more familiar with how corporations operate, so that's something you should think about as well. You can have two entities that are protected from the liabilities of each other, but whether that would be worth your while would also depend on whether you are okay with extra costs of maintaining two legal entities, although it appears to be a good idea to protect your other...
You should get married and apply for a green card. I don't know if you can get it in time, but depending on how long since your visitor status has expired, you may be able to get advanced parole. If the unlawful stay is more than 180 days, then you should not travel abroad until you actually get your green card or LRP stamp on your passport. You should consult an immigration attorney immediately.
Sounds like you may have a cause of action based on, among others, California's Unfair Competition Law (CA Bus and Professions Code 17200 et seq.) You should consult an attorney experienced in business litigation.
Yes, you can. Other than competency, you should consider costs and convenience. Hiring attorney near you would be a good idea, but I often hear people having difficult time communicating with their attorneys, even though they are near their attorneys. Thus, hiring an attorney near the court you will file the suit may be better. If it goes to trial, it may be inconvenient for you, but at least it would cost less of you to travel than your attorney. Good luck.
I agree with Mr. Khurgel as far as immigration law is concerned. For marriage, however, you should contact the county office of your residence and ask what kind of documents are required. As long as the marriage takes place under the law of its celebration, most likely your state's family law, USCIS honors that as a valid marriage. In general, as long as you are a resident of the county, the requirements are pretty much the same regardless of your finance's current immigration status.