My three best runs (and the final one) have been with that initial setup and the same path: Ally Mossi, Benin and Zazzau, rival Oyo and Dagbon, have Oyo only ally Dagbon. Get diprep as your fetishist cult.
I could declare on Oyo, with only Dagbon as their ally. I've encountered two options: either Mossi and Benin are willing to join, or Zazzau and Benin are willing to join, call them in with promess of territory. Give the southeast province to Benin so they border Nupe, the northern provicne to Zazzau or Mossi, get the other two, you now border Nupe too. Full annex Dagbon (either as non cobelligerant, or cobelligerant if they had no meaningful ally). That's extremely important, that "unlocks" you by giving you new borders, and that allows to call Benin against Nupe.
You now border your allies, Nupe, and Bonoman. Bonoman is usually allied to Mossi, so you need to call Mossi in another war, likely with favors, or wait until Mossi dishonors. In all my games, Nupe was allied to at least Katsina, and sometimes someone else (Yao in my successful run). Call Zazzau and Benin in, they'll both border Nupe and will likely rival. Get provinces from Nupe to get a border with Kano, break the alliances of the allies of Nupe. Kill Kano to border Katsina and Kanem Bornu, Kano usually have no allies (and in my last attempt they were actually already dead).
You now unlocked the east, Kanem Bornu and Katsina are relatively easy to take, and things will likely start moving because you destroyed the alliances, so Yao, Air, KB and Katsina will usually go to war with one another. You can pick their remnants any time. It should be time to get Bonoman, which means you border Kong, or more likely Mali who ate Kong. That's something that should be replicable consistently if you have the initial setup I mentioned, and be done relatively quickly. (by 1460 I'd say).
I went quite heavily in debt for my first wars but started swimming in money from the second one, by getting 100 ducats from each of Nupe, Katsina and Yao. As peacedeals is your main source of income, I found it more useful to give the first provinces you conquer to the nobility and not the clergy as one usually does. You want force limit more badly than you want money, and you have to increase autonoy because you can't afford revolts that would delay you too much. Later on, once you take the goldmines and develop them, you have a massive income to support the mercswarm (the issue is not so much the wars than the 20k men constant rebellions in Sunni land, so you have to use mercs or you'll run out of manpower).
Then, I guess it's time to look for new alliances depending on who is strong, who ate who, and who rivalled who. In my successful run, I could rival Mossi at that point who became irrelevant and just blocked me, and then ally their rival Songhai. Luckily in my game, Mali was only allied to Songhai, and Jenné and Macina both rivalled Mali. I think I was allied with Zazzau, Songhai, Macina, Jenné and Yao (Benin rivalled me). I don't know in which order I proceeded, but I ate Kanem Bornu and Katsina. Soon, Songhai had revolts and the combination of their opinion of me and their revolts meant they dishonored against Mali, I called Jenné and Macina, we crushed Mali two times in a row (the second time I had also allied Jolof). That's where I did a mistake, I was fighting wars in the east and dealing with revolts in the Sunni land taken from Katsina and KB while my allies fought Mali, and I let them get the occupations. I said screw it, and I full annexed Mali in that second war, feeding their land to Macina and Jolof who had the occupations, which is why I had to trucebreak to finish them.
At some point, Jenné attacked Songhai and called Macina and Timbuktu, I dishonored and everyone ate Songhai: Jenné, Timbuktu, Mossi and Zazzau. I attacked Mossi, released Songhai as a vassal.
I think at that moment we were around 1480 and there were almost exclusively my allies left. There was probably Jolof, Macina, Jenné, Timbuktu, Mossi, Zazzau, Yao and Benin, with only Timbuktu, Mossi and Benin not my allies. That's the point were things were really easy. I betrayed my allies one by one, doing reconquest wars for Songhai cores to make things cheaper. Yao, Zazzau and Benin were free to pick, Mossi too. At that point I had two alliance webs to face, because Macina and Jenné ended up rivalling each other. Jolof was allied to Macina. Jenné was allied with Timbuktu. Morocco was allied with both Timbuktu and Jolof. Jolof was 80% WS, Macina 140%, Jenné 80% and Timbuktu 45%, or something like that. That's what I mean when I said I overfed Jolof and Macina. I knew I would have to trucebreak Macina anyway so I kept them for the end. I attacked Jenné, full annexed them and Timbuktu as non cobelligerant. We were around 1490, and I wanted everything by that point (I had started integrating Songhai). That's why I just broke Jolof from Morocco instead of taking their Sahel provinces they had gotten from Fulo (I could have done that and avoided the extra trucebreak, you don't need the coastline). I got 100% from Macina, then trucebroke the two of them as soon as I finished coring (to avoid keeping provinces I can't core because I'm at war with someone who had a core there). So I could have saved a few years, but that would have meant I'd get 200% overextension, -3 stab and 10 WE at the same time. Let's avoid that if we can
I finished right after getting mil 7, so I could use cannons for the final wars.
Overall, the beginning is relatively straightforward with the good setup. The key is really to be able to get Oyo and a border with Nupe, and give Benin a border to chain wars immediately on Nupe. In runs where I could not get Oyo but only Dagbon, I was way too slow, and in one run where Benin did not want to join against Oyo and thus did not border Nupe, I lost against Nupe+Katsina+Air because I could only bring Zazzau. Another opening could be to go on Mossi immediately by trying to ally Songhai, but I have not explored it because Mossi usually had good allies at start, and I found good success with my starting moves.
Be mindful never to betray your allies, always give them land, you can't afford to be unable to call them in for several years, that fucked one of my runs. And set provinces of interest before the war to get the occupations.
I think I got to the point where I have to abandon Mossi and I border Mali 3 times, but in two of them Mali was too strong and had too good allies. My final one was successful because everyone rivalled them. In one of the others I was completely locked and I think I messed up. In the other one, Mali was allied to Jenné and Songhai, so I tried to go on Mossi, and later on call my ally Songhai against Jenné, but Mali declared on me during the war against Mossi and Songhai dishonored.
Basically, there are two turning points: initial setup, and how things look once you border Mali and built a powerbase. If you're lucky with the two of them, you can do it. Once Mali is dealt with and you cleared up the east, you're the uncontested superpower and you just have to betray your allies in the West/the North.
Generally speaking, important thing is to use mercs, at least after your second war, and to slowly increase their number by consolidating infantry after every battle and replacing regular with mercs. Manpower was tense early on. Increase autonomy BUT give provinces to the nobility, as I said. You can't lose resources on revolts early on, and as I said, you'd rather have Force Limit than tax income. Sunni land around Katsina will revolt anyway, and you want to decrease autonomy on the goldmines. That's the point where you can handle the revolts, the goldmines give you enough income to throw mercs. I developped all of them to 10 prod. The rest of my dip went in doing separate peaces, integrating Songhai and buying WE (you're constantly at war/in revolts, often with several wars to bypass alliances, without access to DotF or any way of reducing WE). My admin went in developping goldmines so that they could reach 10 prod, coring everything and stabbing 5 times at the end with the overextension and lack of religious unity. I focus on admin early, or else you can't get to +1 stab and core the Oyo + Dagbon + Nupe + Kano and you have to sit on OE. Then on mil. I get money from burghers and 150 adm and mil every time it's possible. Keeping forts you conquer can be a good idea to avoid the spread of separatism in the North East while your armies fight in the West. There are ones in Kanem Bornu, Katsina and Air on game start iirc, and that's the land always unhappy becaue they're Sunni and you won't accept their cultures (accept the cultures from the goldmines, obviously).
I guess I was lucky that I could avoid fighting Morocco, and that I had two 2 siege generals (rolled several ones, got others from nobility (you can safely ask for generals because no need for a diet, they'll be happy from you giving tons of provinces)). My ruler died in 1475 and I fell in a real regency for 9 years even if my ruler was not a general. I'm not ashamed to say the game instantly crashed.
That's exactly the achievements I like. You never face insurmountable odds but you are so pressured that you can't afford to lose any resource or to take too bad of a decision. Every ducat, monarch point and manpower count early game, and there are real choices you usually don't do, like "do I use more men to siege that fort to get more participation and thus more money in the peacedeal, or do I park one unit and let my allies siege it to save manpower?". There is not a lot of micro skill required after the first wars, but a lot of game knowledge to minmax resources and get around alliances. There is an element of luck but it's not that massive (It's not Electable --'), it has flavour (I'm getting seriously bored of the "start as an OPM and blob" ones, especially if they are more specifically "start as an OPM near the Ottomans and blob"), and there is the threatening timer. In many aspects, it's similar to Manipur as you are the weakest nation of a medium-sized area and need to unite it. No wonder both stand together at the top of my list of funniest achievements so far (alongside a few others).