Just buy a Heinkel?
The Heinkel Tourist is the most user-friendly OddScoot available. Tools, spare parts and literature are available from the Heinkel Club Deutschland. Join the HCD!
The next order of business is to join the "Heinkel Tourist Scooter Group" on Facebook. There are a fair number of Heinkel owners that lurk on this site.
If you don't already have a workshop manual, download one from this site or buy one. Can't find one? Check ebay. They pop up often.
Next, buy a 12-volt battery tender. Heinkel Tourists use a battery assisted spark system which requires a battery. Additionally, the starter relies on a battery. If you think push starting a Vespa was bad, the 330lbs of Heinkel will really cause you to sweat.
Lastly, start making Heinkel friends. Heinkel Tourists have their own quirks that may require a fair bit of friendly counseling.