Porto-Novo is the capital and Cotonou is the government seat.
Nigeria Depends on the area you consider as 'West Africa'. Mauritania is marginally bigger than Nigeria, and if you are prepared to consider non-coastal countries, Mali is even bigger. Look at a maqp of Africa and find out what you consider as 'West Africa'.
Gulf of Guinea
The capital of Nigeria is Abuja. It originally was Lagos.
Including islands, Cape Verde is the westernmost country in Africa. On the mainland, Senegal is the westernmost nation.
Egypt is a country not a capital city. The capital city of egypt is Cairo.