1. I go by feel. If the sole feels really squishy that means it's almost through to the cork; at that time I consider it time for a resole.2. Cuffs are traditionally a casual "country" detail. I typically put them on flannels and tweeds, and sometimes on suits when I want to go full #menswear. I generallly wouldn't put them on a more formal suit, but it's sort of a personal preference these days I think.