Shell, James Bryant Conant said of progress: "Behold the turtle. He makes progress only when he sticks his neck out." You have made the correct first step in writing -- you have written. As one who edits for college faculty writing for publication in refereed journals, I often advise, "Just vomit everything up on the paper. We can clean away the stuff we don't need. But if you edit yourself as you go, you'll never get done." I know the physical discomfort that goes along with that first "getting it all out." There is no right or wrong way to begin. You just do what you have done -- begin. Your original posting is, in and of itself, your outline for developing your fascinating story. As this particular forum touts itself as existing for the honing of the writing craft, it certainly appears you're in the right place!

Now in keeping with the purpose of your having stuck your neck
out :-), I will offer these suggestions. Now that you've begun -- take one (or two) of a couple of approaches (depending on whether you're an essayist, a reporter or a story teller): Go back and add details (facts?) to what you've written. Dates such as when this division by the French and the Catholic Church was created, which census you are referencing, why there is a connection between the end of the slave trade and the Watusi who was never a slave, who were the people advising you about interacting with the king, why/how long the king has been in exile,etc. From a technical aspect, research should be replicable, hence the need for details - names, dates, places.
But most importantly, and you gave us a glimmer of this when you mentioned the loneliness of this kind of research, give us (the readers) more of you -- your highs as you made connections, your lows when you ran into dead ends or where warned off your connections, what drives you beyond the memory of the story of your ancestor, people who've helped/hindered, family reactions to/support of your quest, etc.

Again, you're off to a good start -- you've started! I wish you great success in your efforts and look forward to hearing more of your story.

JS