My quarry is now basically finished. It has a horizontal area of 1200 blocks and is 60 blocks high. That took a while, especially since I used stone pickaxes almost exclusively.
So now I have 44 diamond, 109 gold and 529 iron stockpiled. I only have about 300 coal remaining though because I used up a lot to smelt cobblestone.
Part of what I used that for can be seen here:
I tried to make the sky structures a bit more "realistic". I'm not really satisfied with the support for my greenhouse though. It looks a bit massive now, but the four single columns I had previously looked bad as well.
nice to have a minecart link from my spawn to my house though. I just need to figure out switches since I currently need to change tracks once.
Since the update my quarry has become a dangerous place though. Lots of creepers and the like spawning there now and due to the layout, you can often not see them until it's (almost) too late.
I've started a new quarry which will be much smaller vertically, but more spread out horizontally. It seems that placing torches every five blocks or so is sufficient to prevent spawning even ten blocks above adminium. I don't know if that's the maximum, but it works for now.