Where to start... where to start?
You ask good questions. Here are some more, and a few answers:
Patent protection only gives you the right to pay for a lengthy legal battle when your idea is directly and all most exactly copied.
Do you have a realistic business plan with both financial projections AND cash flow projections? Not a pretty little document that you do to satisfy someone else, but a thoughtful analysis of what your business will require to be successful. Writing this down helps focus the founders on the ugly boring stuff that otherwise is lost in the glammer of a startup.
For most small businesses, QuickBooks is the most common accounting package, but it is weak for manufacturers trying to cost and track WIP. I know of no good, inexpensive package for very small businesses like yours. So use QuickBooks, but be aware of its limitations.
Have you thought of the human side of the business? You and a partner sharing the work. Who is responsibile for what? will you both hold other jobs too? what are you inidividual strengths and weaknesses? What additional people are needed, how will you pay them before sales happen, what personality traits does each job require? Who will manage them?
How do you know customers will like your product? (Don't expect others to share your personal likes.) What kind of market research have you done?
What is the structure of your business, and why?
That should be enough for right now. Good luck.