Looks cool. I'm personally not a fan of veggie stuff but I am an Arduino fan. Here's a link to my Arduino/Android engine instrumentation project -
http://www.peachparts.com/shopforum/diesel-discussion/350205-engine-instrumentation-project.html
I later added a fuel pressure sensor to the system -
http://www.peachparts.com/shopforum/diesel-discussion/362989-adding-fuel-pressure-gauge.html, which is something you might be interested in as I understand veggie fuel is tough on filters and an early warning of clogging would seem to be helpful.
How are you powering the Arduino to deal with the dirty automotive electrical systems?