How many pettiocoats in the 18th century?

[frualeydis]

If I'm going to finally make something from the 18th century during the NaCoFiMo I need to find out how many petticoats I need. I have a shift, a pair of stays and pocket hoops. However, I think I'm going to settle for something like this (the style, not the fabric, but I couldn't find a photo of the dress I want to use as inspiration) and then I should use a pad instead I think.
But the question is, how many petticoats? The visible one of course, but aside from that?