AC+, like any insurance, is something you have to decide on for yourself as to whether it's "worth it" -- reason being everyone's situations are different in terms of how prone they are to accidents and how impactful an out of warranty service chaw would be.
As for 128 vs 64, buy what you need but no more than you'll use. Paying for unused storage is a waste as you get little of the price difference back when you trade or sell the phone in a year or two.
My choice was 64, no AC.