...or can you assign them a "tomb" after they're already dead and it'll bury them there from the corpse stockpile?
You can't assign tombs after death. I assume he does it in advance.
I am curious about the layout of the rest of your fortress. Do you have pictures of it?
The rest is mainly arranged on the vertical around the staircase, and is just a random mess, so doesn't look all that great. But my bedroom complex is kinda neat:
(The extra staircases are part of the plumbing.)
This is my 'Forgotten Beast Reception Area' (under construction):
Those patterns are incredible... my square fortress is put to shame. What tileset is that, by the way?