1 agree
2 yes, heavier is less recoil.
3 balance is different with loaded mag but yes they are top heavy
4 I much prefer .40, especially from 4" or 3" barrels, either will work most of the time but 40 has more power without being harder to handle.
5 4" for a gun you may carry, for home defense, either will do. The velocity difference will be larger in 9mm than .40 in my experience due to different powder burn rates.
6 personal preference. Stainless had advantages as far as maintenance, mat black is harder for others to see in the dark.
7 Can you really put a price on your wife's happiness?