Lots of advice. I would add only this. Protecting intellectual property is always a problem and particularly for a small business. As has been said, for someone wanting to reverse engineer and steel your ideas, it would be a simple as buying the product and copying it. If they were really sneaky, they would have a third party do the purchase to isolate them from you. Several of the companies that I worked for in the past used similar tactics.
It is possible to avoid consequences of legal action buy acquiring a product of interest, having a third party tear it apart and write a complete set of specifications to be able to design the competing product from the specs, fire the engineering team, and have a second team design a product from the derived specs.
Assuming that you have no protection by virtue of patents or trademarks, your only protection would be trade secrets. We used trade secrets ot protect intellectual property regarding the manufacturing process as we felt that it would be virtually impossible to for someone to determine how the product was manufactured through reverse engineering. That probably wouldn't work well in your case.
I would suggest that you look into dealing with them but having a very strong non-compete/nondisclosure agreement in place. Whenever we dealt with a third party vendor, we had such agreements in place. Even the job shops that outsourced to. Such an agreement would accomplish two things; if they are truly interested in partnering with you, they will sign it. If their intent is to steel your design, they will balk at such an agreement. Of course, that doesn't mean that they won't try to buy you out at some time in the future. We had a small startup company with an innovative new product. We entered a supplier agreement with a Fortune 500 company. A few months later, they made an offer to buy out assets. We finally reached an agreement and sold for $13M. All of our employees, including the CEO and myself were hired by them as part of the technology transfer agreement and I was able to retire two years later from my share of the proceeds.