Hi RedHouse, I'm glad you enjoyed/are enjoying the quest.
Judasrising, Vravelo, I'm happy you are still here and even help players new to the quest!
Peril Beam Badge:
Just north of the southwest corner of the main overworld, in Ink Swamp there is a shadow. Lightbomb it. Then you can fall down to a part of Dimly Lit Caves where is the stone to push. It has floor markings on both sides.
Quiver 4:
Actually, I see that it's where Judasrising shows it and I don't see any serious obstacle. Seems like you either go through the teleport from the graveyard or normally through the tower and in the last case you need Din's Fire and a Super Lightbomb.
Last medal thing:
It should be "Farore's Wind" and its ingame name is probably "Blank Medal", but I don't find it in the item report. So it might be given with a script or in a conversation.
I always put the farore's wind item at the end of quests as a completely optional thing, so it might be something that you receive when you play in an extreme way (like, beating all towers before beating the first dungeon) or hidden in a high level secret dungeon or awarded in the final dungeon when specil conditions are met.
For example the last part of the true final dungeon has a chest on the right. Its contents depend on how you played and I remember some has very special conditions (like getting a very rare item, but not getting an easy to find one, etc.). So the Blank Medal might be one of the very special awards there.