First off- this is not my cake.

im making a cake similar to this but don't know what kind of flower this is. Also why does it look plastic? How can I make it look like that? Was thinking of doing a gumpaste peony instead. Any thoughts or ideas?

its a fantasy flower. You could make it with a 5-petal cutter, as for roses. The shine could be from luster dust or just steaming. 

Yes, what the other poster said.  Once you cut out each layer, just ruffle the edges some and stack up the layers.  Looks to me like they used 2 layers, then a very small one in the center.

Yes, most any large flower can be used unless there is a request for *that specific* one :)