Typically, these are youths or mid-aged people from developed countries looking to make meaningful contributions to society. They pay their own fares and are hosted by the Nonprofits running the educational programs. Should I start an organization that matches respective programs with volunteers? What sort of legal registration would be needed? I was thinking donor organization. Would it be possible to run it unregistered for the start while trying it out?
Lots of different questions here.
Volunteers are not considered donors in that they can't really deduct their volunteer-related expenses as donations. Nor can the entity claim them as revenue, unless the volunteers donate to the nonprofit and then the nonprofit buys their tickets.
In general, the last thing we need is yet another nonprofit. Why don't you try finding an organization with a similar mission that could partner with you to see if it works?
For example, you essentially become a self-contained department within that charity. You then recruit your own volunteers and donors, run everything through them, and… If you actually need to stand alone in the future… You can separate as an independent organization at that time.
But this way you will not need to setup all your own systems, file your own tax documents, conduct your own audit, etc