Dr Oetker Flan Creme Caramel Dessert, 3.7-Ounce (Pack of 6)

Do they need to be kept cold until served?

17.99 includes how many boxes or packets in total?

Can can you can make this Flan using long life, shelf stable milk? I know it works ok on the mousse, but this requires heating. Thanks.

I have this arriving on 8-17. Do I need to add vanilla baste or is it okay like it is?