I wonder to what degree insurance is mandatory, once past the EU borders.
Perhaps, those old pilots who "flew a Tiger Moth at 600ft to Mongolia" (as repeated in the airport bar) did it in a different era...
I'd also carry a bootload of spares. A vac pump, spark plugs, a full toolkit, the full service manual (the ATP CD)...
An EPIRB with a built-in GPS is essential - in much of the world there is no S&R and you will rely on commercial shipping being sent the message with the coordinates.
That's an amazing project FF, if you are serious! What plane?