[Routine help] Mad Hippie Vit C Serum .. how do you use it?

Hi all! I've just bought the Mad Hippie Vitamin C serum, heard lots of good stuff about it. It was rather expensive and I want to make sure I use it right.

How many drops do I need? Does it require your face to have a certain pH - and if so, how do I reach that pH? Do I have to wait until it dries to use other products? Where in my routine should I use it?