Firstimer, first of all let me welcome you to the forum. Lots of good info to be gleaned from these pages!. And believe me when I say most everyone here is excited for you. This is better than a new car.
I'd say that the other posters about covered it, especially the 30 amp surge protector. Also, we kind of favor the Rhino brand sewer hose. Mainly stay with a good quality hose.
A now infamous member of this forum has quoted in the past "an RV should be roomy enough for drinks for six, dinner for four and sleep two." Kids that age belong in tents. And company belong in their own RV, motel rooms or whatever.