Lighting design projects should always start as a collaborative process. You might have a clear and detailed vision of what you want. You might be utterly clueless. Either way, it’s wise to get professional guidance from the beginning. The designer’s job is to ask questions and help flesh out the design and scope of the project. They’ll help you determine how you want people to experience your space. They’ll ensure the design is both functional and attractive. One of the most important questions they’ll ask is, “How much are you willing to invest in the project?”
You need to be upfront with that last question. The designer needs an honest, realistic budget. It determines the scope of the project. It doesn’t do either of you any good working with false figures.