Recently, when trying to get some info about Mor, the main language
of Burkina Faso, I encountered interestingly related words in that

  Town name:     Ouagadougou
  Dialect name:  Ouapadoupou

What's the system behind the relation of these words?

  Lang name:     Mor
  People:        Moaaga (sg), Mossi (pl)

Again: how do these derive from what roots or stems?

I'd like to know some principles of how this or the grammar of related
languages work.  The gives the classification:

  Niger-Congo, Atlantic-Congo, Volta-Congo, North, Gur, Central,
  Northern, Oti-Volta, Western, Northwest.

Does anyone recognise something typical in grammars of languages of
these kinds in the above examples?  (Some languages I knew of from the
Niger-Congo family, which I assume are better studied, would be Igbo,
Ewe and Yoruba, but I don't know how closely related languages in this
family are).

Another (related) language I'm particularly interested in is Atti (a
native speaker pronounced that as [a't_j:I], I think).  Seems quite
small, so I did not even find a primer.  Its an Ivory Coast language
for which the gives the following classification:

  Niger-Congo, Atlantic-Congo, Volta-Congo, Kwa, Nyo, Attie.

And: where can I find information about tone languages that are
described as 'registered' tone languages (like Mor), that seem to be
frequent in Afrika?

I'd appreciate any information! :-)