The wording says Supernatural Virtue or Ability "that only affects himself" (presumably to rule out magic weapons of Entrancement or Hexing) and then gives an example using the General Virtue Puissant Single Weapon. sigh. The wording and the example go against each other - however, as the examples of lesser craft magic in Rival Magic just says "A character with a Virtue that only affects himself (eg Greater Immunity to Fire, Puissant Single Weapon)" I think your reading of a supernatural or general virtue that only affects the user, as long as they need the item to perform.
I would be fairly strict in the item being something you use to perform. A shield is used to perform Puissant Single Weapon as it appears on the Melee Weapons Table in ArM5 p176 as a weapon using the ability Single Weapon, (it's damage is +0 so if you try to smack someone in the face with a shield bash you only use your attack advantage and strength for damage), and a shield is a perfectly valid specialisation for Single Weapon according to p67.
For your examples - do you really need any items to read a book or study a skill independently? Like with items of quality as made by Verditius, you need to show that the item definitely works hand-in-hand with the activity.
What item would be appropriate for Immunity to Fire? I would say the heat-resistant gauntlets and apron as used by blacksmiths and glassblowers when dealing with molten-hot materials. To be fair, you may be better off using method #4 if you have the right materials.
Confidence - I've checked the errata, and the reference to confidence is deleted so I don't think you can use confidence.