The first plagues of triangles were random and simply released over an area. Those exposed to the spores would have the triangles grow wherever they could find root. And no, there is nowhere where it couldn't take root on the outside of the body, as long as they could establish a root without killing the host.
The most triangles on anyone, to my memory (not having read past where Sigler is up to in the book) were on Perry. Average, who knows? In contagious, Sigler doesn't always say how many triangles each host that we come in contact to has, and there are plenty of hosts we never see.
And to answer your first question, Of course! Perry survived! Isn't that better than the others?
-You thought triangles were bad under your skin. Well, try a yak.-
-You thought triangles were bad under your skin. Well, try a yak.-