16 Galena.
Well, it was quite a ride towards the end. The engineers said it would work but that kept looking at me funny when I said we should be done by Granite. When we finally pulled the trigger, it was nearly Galena, and for three weeks the fortress was hauling dead goblins and their gear out of that hole. The hydra, as well. I think we might be fortunate that we chose to wall in the entire enclosure securely with no doors or even hatches, floodgates, or bridges. When that Hydra came out of his cage underwater, he went berserk. I don't think he drowned though, the 84 other creatures in the water with him were all attacking him. The hydra corpse is in the corpse storage area. I'm not sure if the butchers will handle it though, since it wasn't killed by a dwarf. Butchers have some mighty strict union rules.
In order to facilitate cleaning up the trash that might actually be useful, there is an armor and weapons stockpile near the barracks area, 2 levels down or so. Bins are not allowed, so you can easily see everything and accurately determine what you want to melt.
The artifact lever in the mayor's bedroom is NOT hooked to anything - I just needed a place to put it while we were installing 300 mechanisms in the goblin pit.
The animal processing area needs some more consolidation. We have butcheries and tanneries spread about a good bit. There's a good start about halfway down the fort. Useful refuse one side, refuse that might rot on the other. Butchering shop in the middle. Food storage as well - plenty of room to mine out some more space, put down floors to quickly get rid of the rock then make a serious food handling complex - what we have now is very inefficient.
I believe I've stopped most of the infinite production lines, except the one for bins, which will only last until the wood runs out again.
If you need to get rid of some rock, build floors - it's the fastest way.
The archery squad is acting mightly weirdly. I tried to put a hunter in the squad, and the squad leader made him a wrestler. The look on that hunter's face! I pulled him back out though, I'm not putting an archer in a squad so he can play melee. There were two well-skilled hunters in the last couple waves!
((The animal storage is also acting weirdly. Cages are not being drawn from them, and creatures are not being returned in their cages. New animal storage areas have the same problem, they are simply not working. Your dwarves do seem to pull empty cages from the depot if there are any there, to fill traps with. Either that or they are pulling cages out of thin air.))
In the last few weeks before I pased the torch, there was another artifact! Usitharoth - a goat leather robe. I was not terribly excited, though it is a nice looking robe!
((Before I pulled the lever on the goblin killer, I was at 34-35 fps with 60 idling dwarves. At human arrival, three game weeks later - 15 fps with 6 idlers, but improving.))
I believe all dwarves are assigned to the "Indoor" burrow at this time.
I believe all dwarves have a personal bedroom, but the most recent wave of immigrants might not.
The jail needs more cages or chains.
Our mayor seems to like tin and windows, watch out and save some tin back without alloying it.
Best of luck, if you have any questions about what I did, I'll be around.