Legacy engrams decrypt year one engrams to complete collections. Non legacy engrams decrypt at 290 if your light while decrypting is less than 299, if you're 300-309 they have a chance at decrypting at 310, if you're 311+ they will almost always decrypt at 310. You can equip one armour, one weapon, and technically class items because they have the "life exotic" perk. But for all purposes two.