You are correct that the blessing ceremony is a one way trip.

The most knowledgeable person in the game when it comes to jewelry would be the dwarven jeweler in the dwarven halls...

The other necklace you have is an easter egg; the initials C.B. are for Cattie Brie, a friend of Drizzt, a drow in Salvatore's fantasy books (and also in Baldur's Gate).

You are not missing anything, besides maybe a bit of experience, by drinking the exquisite wine. The quest log gets cleared in the wastelands, so just ignore it.

Did you get the letter dropped by Pedro in the sewers under Ars Magicana? Did you take the letter from the cave? Lt Robin in Ars Magicana should arrest Tingalf once you bring him this evidence.
Marcus-Tingalf-Trevor-Quest

There are 4 treasure maps. Silver Armour and Treasure Maps


You could have changed the name during when you started the game. You can hex edit a file to change it afterwards, though; character name.

You will not be able to return after the ceremony (except by hex editing), so sell anything you do not want and take everything else with you.

Stats are random, even with the dragon armour.
If you quick save before running your mouse over an item/chest/merchant or hitting the alt key, you can identify the item or trade with the merchant, then quick load to get different stats or inventory. This can be done repeatedly to get the best stats or specific bonuses on an item (save after finding good candidates) or looking for specific items (such as spell books or charms) from merchants.

The dragon shield is the last piece (no leggings or boots), and is located in Stormfist castle. The first time you wear the complete set you get experience, learn a level of a spell and Bless it cast on you (temporary). There are no additional bonuses for wearing the complete set.

The Singing Blade can potentially be quite good, but has no other purpose than whacking monsters with the pointy end.

The silver breastplate upgrade is related to the treasure map quest; see the link above.

None of the quest items can be used for other quests / purposes. The toy dragon explains how Janus found the Sword of Lies, but is not part of any quest.