Marco,
Is it also possible to set this up behind a firewall?
Yes; with the caveat that your wiki must be running Parsoid. It is also
theoretically possible to still use Print on Demand services behind a
firewall as we can POST a zip bundle to them -- likely however you'd just
disable that functionality and I'm not sure our new bundle format is
entirely compatible with the old bundle format...
If you want to set this up locally; I can help with that if you jump on IRC
#mediawiki-pdfhack on freenode. I'm mwalker.
~Matt Walker
Wikimedia Foundation
Fundraising Technology Team