Be sure that any contract work you have done is covered by a contract agreement that includes a non-disclosure statement, and a statement that any inventions created under the contract are assigned to your company. Again, get advice from your lawyer.
And be sure that your contractors qualify as contractors. Companies have gotten in trouble by hiring as contractors people who otherwise looked a lot like employees (but didn’t get benefits because they were contractors). State authorities may decide that your contractor is really an employee, and accuse you of hiring them as a contractor just to avoid paying benefits. An employment attorney or an Human Resources professional can help you keep out of trouble, so get some advice to make sure you understand the difference between an employee and a contractor.