To those curious about the Gilding Process, without getting into the mechanics of it, this is what Johann Gilded:
Fingers and Toes are cosmetic, so he did them as part of Hands/Arm/Feet/Leg. Hands and Arms are separate processes, the Hands improving manual dexterity and the Arms improving Strength and increasing the Armor of your arm. The process is separate for each hand and arm, and I'm pretty sure Johann did it for each hand and arm instead of skimping on any of it.
Feet and Legs are also separate, and a separate process for the left and right ones. Feet grants bonuses to resisting fatigue on travel by foot, and leg grants armor of the Legs on top of boosting Movement. He probably did every single one of these.
There is no Torso Gilding in Realms of Sorcery for some reason, but I'm pretty sure that it should exist and Johann took it. He also took the Lung gilding which means he doesn't even need to breath air, which he told Mathilde that he uses on solo ventures, probably by using gas.
The Lung one is dangerous if failed, as it causes you pain every time you breath if you fail, but then we get to the very delicate part. The Head. The Head can either be done all at once, or separated into components such as Ear and Nose (eyes aren't included in the book for some reason, but it's clearly a thing). Ears improves hearing, Nose improves smell, and Eyes would logically improve sight. Head lets you gild everything at once, giving you the benefits of everything being gilded (improved senses overall) as well as boosted head armor. The downside is that it is one of two Gildings that results in instant death if failed.
There is another very dangerous gilding that results in instant death. The Heart. If you Gild it then you no longer feel emotional pain, which let me tell you I'm not sure if that's worth risking death.
The book only gives guidelines for these modifications, but you can get creative and gild more parts I'm pretty sure. The only ones in this list that are left for Johann are the Head ones and the Heart. After the disaster that happened with his eyes, I'm not sure if he's keen to possibly ruin his other senses, and I'm not sure he should risk death for the Head. The Heart is not worth it. Maybe he can do Liver or Kidneys or Intestines I guess. I'm pretty sure bones and muscles are linked to the limb in question so I don't think you can gild them directly unless it counts as a separate "organ".