The first film could open with the Battle of the Powers in full swing. Then we’d take a step back, with a Vala (Mandos?) explaining why this war was fought, explaining the creation of Arda and the awakening of the Elves. Then the capture of Melkor.

The mostly peaceful Great Journey would be a nice break after the action of the war. Thingol and Melian’s meeting would also be a critical thing to include. The Great Journey could conclude with the Eldar crossing the sea on the island, then a few thousand year time jump forward.

The elven civilization of Aman is now in full bloom and rhe focus is now on Fëanor, who is already s reknown master of many crafts. Melkor is released on probation and things go bad. The Doom of Mandos might be a better cliffhanger, cutting off at the Oath would leave the impact of Fëanor’s bad choices stunted. His “from the best to the worst” - arc would have the maximum effect wirh him ordering the first Kinslaying and betraying his brothers by burning rhe ships in the first film.

I’d say that two thirds of the film should be about Fëanor and Melkor in Aman, with the bombastic war of the gods in the beginning that should have enough intrigue for general audiences.

And yes, six films should be minimum to give justice to the overall story of the Silmarils ;)