Depends on what type of NDA you signed at employment. In this day and age with the proliferation of AI and free programs such as Canva and the like trying to start your own design firm to me is not a wise decision. But you haven't given us any idea of your experience level or what type of firm you are considering, so it doesn't give us anything to form an opinion with.
Very weak contract, but I’d like to try and establish the business a bit before I exit my current employer. I run the current company for an owner. The field is a niche of landscaping but I thought this community would have a lot of parallel experience/advice.