Metals lose electrons easily to form anions. Noble gases have a stable electron configuration, therefore a large negative electron affinity value.
More electrons leads to more repulsion between electrons which leads to a larger valence shell.
Ionization energy increases with every additional electron that gets removed. The smaller the atoms, the higher the electronegativity. Very much ionization energy is required to remove electrons from the stable noble gases. Electron affinity decreases down a group because the atomic size increases.