When discussing mass production with a potential client what legally needs to be addressed?

Remember, that the primary reason business fail is that they are not adequately capitalized.
So, you need to carefully assess your cash needs to produce these goods and to fulfill orders as they come due. You need your cash in place before doing anything. You need to overestimate your cash needs because it is only an estamate here and things can change real fast.
As far as you paying for this, it sounds like this is a joint venture. You need to know that your partner (famous or not) is serious. The only way to determine this is to have that partner contribute capital to the venture. If she will not do so, then you should rethink this venture.

In any event, you need to think about some sort of agreement to set out your understanding.
This is absolutely essential, if you want to avoid headaches and lawsuits and minimize
trouble down the road.

Hope this helps.

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