Help design A Songhai/African setting

[CowardlyPaladin]

I really don't want to make this political or get into political fights about representation or imperialism, I just want advice in designing a setting, no modern stuff please.
I like to run D&D settings that are obviously fantastical versions of real life societies, much like Legend of the Five Rings.

So one of my players is of African descent (specifically Mali) and said that she would appreciate it if we set a game that was in her own culture, and I figured that it would be nice to try that out. Problem is...I don't know anything about Western Africa that isn't broad strokes. I'm a Roman Historian and I know what folk tales, beliefs, legends and history I can draw upon to make a fictional ridiculous version of Rome. But I don't know very much about most regions of Africa medieval history and my friend is only vaguely aware of the region, and neither of us know the language, so I am having trouble getting started. However I do want to try, particularly if it will make my players happy (they are getting sick of Rome anyways)
I've decided to make this a challenge to design a very different type of fantasy game and push my and my players boundaries. And since Gianttip is multi national/multi cultural and full of really smart people, I figured I might start here (and I got a lot of nice advice when I did a similar project with Southern India). Help me design a campaign setting for a group to play in for the next six months that is based on African (specifically Songhai) folklore and traditions.

Oviously Africa is a continent, not a country, so I narrowed my focus to where my friends family came from and wanted to do a fantasy version of the Songhai Empire since I was reading about it and it seemed really cool Now I am not trying to create a super historically accurate recreation of Western Africa, instead I am want to do what was done with D&D, taking some of the social trappings, traditions, legends, and mythology of a time period/region and making a society out of it. If you have ever played the game Jade Empire or Legend of the Five Rings, that is sort of the feel I am going for, just with the common races (and maybe some new races based on local folklore) incorporated into the region.

So this is going to be a massive empire that primarily makes its money through international trade, so there will be a lot of peoples from other countries coming in to trade and hang out. There are very powerful merchant guilds called Julla who work with the monarchy to maintain the intricate and somewhat convoluted trade route. These routes go through quite dangerous regions that are full of monsters, so adventuring parties are often commissioned by the merchants as ways to protect goods from bandits and beasts. These adventuring parties are given a contract and work on commission, though they have to rally into militia units in times of war. In opposition to the Julla are labor organizations, much like Unions (I don't know the local word) that represent the workers, and relations between these two is one of the main political conflict of the game. The various clans/noble families of the empire are organized based upon one particular craft or form of trade, with the family structured around that good (this was apparently true). So one family might be "The metal workers clan" and within that clan you would have various castes based upon your role in the metal working system.

The kingdom has a very extensive prison system built up with the focus being more shaming than punishing or rehabilitation. In order to keep law, special enforcers called Assara-munidios are allowed to travel the empire to see if crimes are being committed and try to root out corruption and inefficiency. They can also be used to fight against demonic cults or sinister cabals. Jurists in this country are the academic elite, and being education almost always leads to a career as an administrator or a law keeper, with massive colleges in the capital city being a testament to that. While local kings can command each of the various regions of the Empire, the Emperor is seen as a semi divine figure and everybody has to swear obedience to him in morning prayers.

Also militarily in addition to horsemen, infantry and elephants, there is a canoe fleet for river travel. That is all I have right now but if anybody has any advice, information I might want to know, or online resources I could access (names would be fantastic) I would really appreciate it.
I'm really interested in how the traditional D&D classes would fit in, and if there are any local folklore traditions that could serve as the basis for some new classes/takes on classes. It would really help.