4) How did the Fe/Ni get into the MW (and other galaxy) halo(s)? into the IGM of rich clusters? If it got there via some 'explosion' or other, by what physical mechanism(s) did it clump/come together to form macroscopic bodies?
The protogalaxies were built of the typical black holes. After the Big Bang these typical black holes intensively evaporated. I described this mechanism in thread ‘Professor Ketterle….’
When the mass of a black hole exceeds the mass of typical black holes then creates disc because the dropping on the typical black hole particles could attain velocities higher than the light velocity. The neutrons placed on the surface of the black hole, in respect of the weak decays, emit the electrons and electron antineutrinos in directions parallel to the magnetic axis of black hole. Owing to the electric repulsion between electrons and to the strong spin polarization of the antineutrinos and electrons in directions parallel to the magnetic axis of the typical black hole, these electrons are accelerated to the velocities almost equal to the light velocity. Due to these emissions the surface of the typical black hole is charged positively. The electric repulsion of protons causes that the protons gather first of all in surroundings of the equator of the typical black hole. At last the electric repulsion exceeds the gravitational attraction and there take place the proton explosions in the plane of the equator of typical black hole. The rapid slow-down of protons creates the electromagnetic radiation. The proton streams carry away some neutrons what causes the additional emissions of electrons and electron antineutrinos in directions perpendicular to the plane of disc. The electron-antineutrino stream have the form of very strong collimated jet. Similar phenomena but on a larger scale took place in surroundings of the quasars. The emitted protons capture the electrons and create the protonuclei, from which after their transformation into the nuclei and electron gas, arise the big stars. Just before the explosion of a big star the composition of the big star is as follows: 80% Fe+Ni, 20% H+He in proportion 74% H and 26% He.
Protogalaxies collected in the supertorus had not evaporated because the number of emitted by defined protogalaxy electrons and electron antineutrinos was equal to the number of absorbed electrons and electron antineutrinos. Before the Big Bang the axes of protogalaxies were tangential to the circle inside the Supertorus.