That is totally up to you.
An itinerary plan can be a list of flights/hotels/activities/restaurants for you to consider investigating further (saving you hours and hours of googling)
It might be a shorter more detailed list with links to click on to book the flights/hotel/restaurants/activities that we’ve identified as being perfect for you. And there will be tips on how to save money on booking what it is you decide you’re going to do.
It could be a revision of an itinerary you have in mind that I can give feedback on – for example I have seen people write itineraries which are impossible and going to cause stress and chaos because they are not allowing anywhere near enough time to actually have the experience. I will go through your plans and give you alternatives and be honest with you if it’s simply not going to work.
What it WON’T be is an itemised, time based, day by day, hour by hour schedule. I don’t believe that’s how you get the best out of New York. I will encourage you to weave time into your itinerary to create space for magic to happen. It’s sometimes the most unplanned, unexpected moments that can be the most memorable – when you hear a musician playing in Central Park and stop to listen for a while then see there’s no line for the row boats and you decide to go for a gorgeous paddle in the lake. Or wander past a cool bar and sit and eat chicken wings and get to know an incredibly interesting person sitting near you or serving you. It might be walking past a theater and seeing a show is about to start and scoring a few tickets right then and there to see something you’ll remember forever. The magic can only happen if there’s space so I will encourage you not to have a huge checklist of things to do. You don’t “do” NYC, you “feel” it.