If you get someone familair with the turf to guide you thats great but it is not necessary.

I don't know how you plan on getting there but if it's on New Jersey Transit be aware that although bikes are allowed on the trains during non-rush hours, if the train is crowded (like most weekend trains leaving NYC) the conductor does not have to permit bikes. So you may be able to get into the city but might have a problem getting out. I don't have any direct experience taking a bike on a train into the city but have taken the train many times and they are generally packed leaving NYC. If this is what you plan some more research may be in order.

What I have done is to drive to Fort Lee (take the last exit before the George Washington Bridge). There is a large public lot and you can pay for several hours. From Ft Lee you can bike across the George which is pretty cool in itself. On the Manhatten side there is a kind of spiral walk that gets you down to steet level.

I did this a couple of years ago when I wanted to buy a pair of Outlier pants and wanted to try them on rather than buy through the internet. (They had a showroom in Williamsburg). I didn't want to kill a day schleping into Brooklyn, and miss my weekend ride just for a pair of pants, so I drove to Fort Lee and cycled to Brooklyn from there.

I got downtown on the path on the west side that extends almost the entire length of Manhatten.
Maybe someone more familiar can offer a better way to the bike path, but I just kind of stayed west headed downtown on whatever street I found, and then after asking someone found this park on 145th street that has an elevator to take you down to the path. It can be somewhat crowded in spots, but you will not be in a hurry so I recommend it.

I ended up crossing Manhatten on Canal which is probably the busiest East-West road on in lower Manhatten so that was a bit of a mistake but it was still kind of fun. I worked my way up to the Williamsburg bridge which is also a pretty cool thing to cycle over.

Bottom line for you is once you get down town you can just discover for yourself there are plenty of bike lanes going north-south so you can take one of those back up to the bridge and you will probably want to go around Central Park for a bit as well.

If you are going to go to Ft Lee. (and even if you are not) I recommend you go on a Sunday. The parking lot in Ft Lee is empty and there is less traffic in NYC.