If you are intending to fly to Offenburg, the nearest international airport is Basel. From the aiprot, take the number 50 bus to Basel, Bahnhof SBB. There you can take a train north to Offenburg. This will take around two hours from the airport.
Offenburg also has good rail links with the rest of Europe, with direct trains running from Berlin.
Minimum age of entry is 18.
Yes, parking will be available for those wishing to drive to Kamehameha Festival.