I have an invention that I want to profit from, but the invention is an add-on component for something that is already produced?

I would highly recommend that you speak to a patent attorney and/or intellectual property attorney

Can a patent attorney steal from you and get away with it?

No if you report the attorney to the right governmental agencies and they take action

I would not use any Chevy logo without securing a licensing agreement from GM.

Do I need an intellectual property lawyer

you can call the music company and ask for the licensing department and get a licensing agreement. I would have an attorney review it.

Can I patent this item, if so, how do I patent it?

you can patent really anything you want if you want to spend the money filing it with the US Patent Office. With that said, your idea has to be new...

Unless the business does exactly the same type of business as the other one the debt wont transfer. but if you are opening another business that is...

How do you sell a sole proprietor business?

I dont see any reason why someone would not want to purchase your business for the "good will" that's associated with it, i.e., your customers.

Should I become an employee of her company? Can I get in any legal trouble if I do what she is asking?

It would appear that you would be acting as what is known as a "finder" and not taking an active role in your friend's business. You are merely...

Breach of verbal contract

I would seek legal advice and counsel from a lawyer practicing in the State of Florida.