Now, on to some of the comments people have made.
First of all, I'd just like to say that it seems kind of premature to talk about merging as many provinces as possible, keeping areas to a minimum, and so on. I know that sacrifices will have to be made, especially as the AGCEEP will probably run out of tags again, and when we must leave out a state, it makes sense to leave out a province associated with it.
However, until we know how many additional provinces that people will allow Africa to have, this seems a bit premature. Personally, I am hoping that if the '300 extra provinces for the rest of the world' figure that I have heard is close to the final result, that it will not seem to be too horrible to let Africa have 30 or 40 additional provinces.
I know that many of you, concerned with only Europe or your own nation, will recoil at the mere thought of Africa having such attention paid to it, but please keep in mind that Africa was a continent with dozens of diverse cultures, and many large centralized states. The number of provinces does not necessarily reflect a nation's importance in world events, but is rather there to provide an EU2 style abstraction of history, and even with 30 additional provinces, the level of abstraction, given the complexity of the history in the area, will be much higher than in Europe. The detail will be much less.
On to some of the other comments:
First, when it comes to Oyo, I think that it should stay. While the Yoruba area was a mass of city states at the start of the game, Oyo managed to aquire a Sudanic-style calvary army, and around 1600, began conquering Yoruba-land. By around 1750, they controlled all of Yoruba-land, a considerable swath of the coast, and had vassalized Dahomey.
As for Benin, when the Portuguese arrived, it was the largest and most stable state in the area, controlling hundreds of miles of coastline.
When it comes to the issue of isolating the coast from all of the African states using PTI, I'll say right away that I find the notion bizzare. It would be like isolating Scotland from England, in order to prevent such 'ahistorical' things as England conqering Scotland, or having many English provinces defect to Scotland. Extremely high attrition rates, which are already there in Regular EU2, can serve to simulate the main barrier to European conquest of the region. A number of medium-sized African states, such as Oyo, Dahomey, and Ashante, did conquer to the coast, and it would seem rather arbitrary to try and cripple possible ahistorical expansion by player controlled nations, for no other reason than 'It didn't happen in history.'