I admit in advance that riddles have a tendency to make me feel incredibly stupid and annoyed.
Riddle 5 is one of those. I can touch adjacent fingers in multiple ways, to achieve the desired results of creating a four finger handed and a three finger hand. What is about those exact fingers for each hand that you mention, "must" be used that I can't see?
I'd like to encourage you to continue your Moorcockian inspired rpg and suggest a few considerations. Your trying something new it seems to me. You haven't touched on what it would feel like to play an incarnation of the champion, or one of his allies or foes. Yet, it seems present just beneath the surface.
A chaos/law psychic world/name generator. Moorcock has stated that he wasn't interested in building worlds like Tolkien, but was exploring his own inner psychic landscape seeking moral answers. The names and features of his landscapes were psychic visions turned into words. Moorcock is constantly struggling with the notion of fate and free will. What are we? What is change? What does it look like? Erekose, Elric and Corum are all tragedies. Corum commits suicide. The evil sentience that is Stormbringer slayed Elric and leapt into a new creation. They are metaphors for something deep within Moorcock. How can a game craft this experience and rise above the swords and sorcery?
Moorcock's use of drugs and specifically his use of acid revealed fluid reality in flux - his worlds of chaos and law. The extremes of each and the illusion of each being separate. The Configurations of Million Spheres is what? Raw possibility, an evolutionary step forward into a new morality free from...?
The Eternal Champion and his incarnations belong to psychedelic sword and sorcery. One can't really copy Moorcock for he was at the vanguard of a counter culture, and that fused to Moorcock's childhood of ruins , intelligence and his attitude is unique to the man.
He utilized intense purple prose to craft an ambient mindscape - the stuff of chaos.
A doom/entropy/ennui mechanic. This is connected to the psychic investigation via the use of heroes as flawed beings that seek.
Fate v. Free Will
The role cursed artifacts and cosmic relics play for a Moorcockian heroes.