Electronegativity and reactiviy

Glad to help!

Ionisation energies and electron affinities are actual values which have been measured and tell you in change in energy when an electron is lost or gained to form an ion (in gaseous conditions) - but yes, I guess you could extend that principle to how likely an ion is to form

Electronegativity is a measure of the strength of an atom to pull a pair if electrons towards itself (however that doesn't stop it pulling more or less electrons towards itself)

Nearly all bonds have some covenant character and some ionic character, Electronegativity can be a factor in the extend of these different characters

With regards to energy, it's easier to think that unless a bond is formed or broken there is no gain/release of energy, so electronegativity itself doesn't not cause an atom to gain or release energy (however, like I said earlier it can have a big influence on the electron distribution in a molecule hence making that molecule more reactive and therefore more likely to for,/break bonds)

yep, each of those 3 things you mentioned have various different factors affecting them - you'll find that in chemistry lots of things are interlinked, it's rare that 1 factor alone can account for an observed function/trend (such as ionisation energy etc)

Sorry, one last thing, you know how the second ionisation energy is greater than the first due to increased effective nuclear charge, would the electronegativity of an atom change after it has already attracted one bonding pair of electrons towards it? eg. in MgCl2?