In addition to limits on imported products, you need to be aware of some costs of importing your potential product in order to determine whether importing that product makes financial sense. Aside from the usual costs of paying for production and packaging, you will have the unique cost of duties. Put simply, duties are fees paid when items are imported. The formulas for calculating duties are very complex and often you will find that a product's duty varies greatly depending upon its classification by U.S. Customs. Duties are imposed based on different things.
Some duties are ad valorem, which means based on a percentage of the value of the imported item.
Some duties are based on a specific rate, which is an amount per unit of weight or quantity. Other duties are based on compound calculations, which involve both ad valorem and specific rates. It is highly likely that you will need help calculating the potential duties your product will face. Your local U.S. Customs office may be helpful but you may need to turn to professionals in international trade. Try to find international attorneys or others experienced in dealing with the most recent version of the Harmonized Tariff Schedule.