John wrote:

Consider this scenario; Using FAA (USA) regulations.

as far as I understand it, yes it is legal, however:

The pilots must be at least a private pilot (not recreational or sport);
61.101(e)(13) and 61.315(c)(10)

Other than that relevant regs is 61.113(d) providing that -- I
summarize some key points, but refer to the regs -- the sponsor,
i.e., charitable organization, notifies the local FSDO at least
7 days ahead of time and in doing so provides some documentation
which includes the credentials of the pilots involved; if
the pilots are private pilots, they must have at least 200 hours
of *flight time* (I don't see anywhere that it has to be PIC nor
that said flight time has to be all in same category/class). The
flights have to be day VFR, no acro, no formation flights...

Now a commercial pilots would necessarily meet these requirements.
As for the other questions however, i.e., flight to another
destination, overnight stay, etc. I don't see it described as
an exception of part 119.1(e)... but, folks who fly Angel
Flights do that routinely, so how does it work? what are the
chapter and verses that apply? or do they operate under specific
Letter of Agreement (or whatever other waiver?)

Note that since you will have to talk to the FSDO anyway, you
might as well as them the question, in addition of course to
asking these nice folks from AOPA,

--Sylvain