How does Niko's cloning work? Would a clone of Sayaka have her power or be an uncontracted potential?
Depends on how you define "Niko's cloning". Her battle-cloning technique is just shaping local materials into magically-controlled, Niko-shaped simulacra-- limited molecular sculpting lets them appear and move identically to her, but a Nikklone pulled out of a wall is still fundamentally a golem comprised of brick and mortar. She
could alchemize an organic, anatomically accurate human body*, but it would be too inefficient for combat purposes, and a Sayaka body double wouldn't be alive/independent, so you'd need an outside motive force to breathe life into it-- a resurrection power
could hypothetically work, but the new Sayaka would presumably be an uncontracted potential.
Kazumi is basically this, except that she was spun out of the salvaged remains of Michiru's witch, with the motive force being provided by its Grief Seed/Cor Malificus. A chimaera is
technically an uncontracted potential, but has inherent magical powers.
*Niko's power is basically FMA awakened alchemy, and capable of remarkable fidelity; she turns
her own fingers into
fully functional homing rockets before using it as an ad-hoc healing power to grow them back using her own body mass.
ED: Actually, if the brain is created in a 'fresh' state and prevented from degenerating with magic (due to the body being in a 'dead' state), then a defibrillator might be all you need to jump-start a new clone.