C.B.
Play dates are usually about 2 hrs - 3 tops. I would definitely plan to provide a snack. Ask the mom for her child's favorites.
As for drop off or stay, let the mom decide which she's most comfortable with. At five, I would drop him off. But if she does stay, you should at least have something to drink and perhaps some little cookies or veggies with dip or something.
Have fun. This will undoubtedly be the first of many!