It is a great place for pictures, but since it is open to the public and I don't think they cater to weddings. Here is a link to some places in Suffolk County, however, that do: https://www.longisland.com/long-island-parks-and-weddings.html
There is a gorgeous park with a lake. There are some spaces that could be good depending on the size of your group. I would try Sunken Meadow State Park, great for sunsets, or Bayard Cutting Arboretum, gorgeous landscaping and on the river.
I don't know, you will need to contact the rangers. They will be able to give you any information.
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