I recently got a book from our University library - "A Colour Guide To Cheese & Fermented Milks" (1995 by R.K. Robinson). This is really a sleeper book loaded with info on tons of cheeses. Unlike most descriptive cheese books, this one has enough info to actually make the cheese.
Anyway, he says that Fontina is an AOS designated cheese. No added cultures are allowed. The AOS standard calls for natural flora (meso and thermo) only. Traditionally it has been aged in high humidity conditions that favor the natural development of B. linens. The AOS standard calls for a 37-40% moisture content. This is on par with a Gouda, so I would press with a medium weight accordingly.