1. Nope, protect is a flat approx. 15% bonus from your base defense, and stoneskin absorbs 10% of the target's maximum HP.

2. Grand Company daily turn ins, leves, collectables level 50-60. (HQ gives double the xp on the first two).

3. The Heavensward 50-60 fishes like Mogpoms, Blue Cloud Corals, etc. used in crafting will probably be worth something for at least a few more weeks until the market's eventually flooded. Pre-50 there's a couple of desynthesis swimsuits obtained from rare fish but not guaranteed, like 10% chance.