Updating My Underground Complex Ideas

I admitted when I posted these ideas that they were old. While it's true that "old" doesn't necessarily mean "inferior," there are some points I would like to update or alter due to my current mindset. Here are some updates I've been thinking about:

In a dark part of the cave complex, they find a door that leads to a finished underground hold. I need to find out what creatures used to live in this hold. The hold isn't populated now. The hold is/ was not a dwarven complex. It's not Skaven. I need to find another underground creature that might have made and live in an actual underground keep.

I've already updated the entrance to be a sinkhole that leads into a large hall. I like this idea so much that I'm making the hall larger and larger in my head to accommodate a day or so worth of investigating just for the one room. 

Now the complex is filled with undead.  The undead are not human, they are undead of whatever creature used to live there.  This could make it doubly scary, a monster and undead in one.

I still like the idea of undead monsters, but they will not be the theme of the complex. Maybe just one section.

There may be treasure there, as the undead keep looters away.  I'll actually have dead looters at random places, killed in ways that undead kill people.  Maybe the party could find the looter bodies before they find the undead, as clues.

This can still happen in the undead section. Imagine a pile of bodies near the entrance that all look like they died trying to run out of the area.

Magic items, potions, traps, etc will all be appropriately aged.  Who knows what a potion 500 years old might produce as a result if quaffed, even if the potion is labeled "Flight". 

I like this idea, and it can remain as-is.

One of my main bad guys, or the main bad guy in my head right now, is a very old vampire.  Matter of fact, he's all desiccated and lying in torpor, shrunken in his coffin.  He isn't controlling the undead at first, because he's not conscious, but once he's awoken, he's in charge!

I like this idea, but just for the undead section. Also, thoughs right now are to make him a Halfling.

Rooms will be filled with everyday items, from the time, just very old.  There could be some masterful weapons, magic items, gems, jewels, coins, etc that aren't decayed, plus an array of decayed items.  'Oh, look!  A spell book!'  The party picks it up and it crumbles in their hands.

There's nothing wrong with keeping this idea. I realize it's not revolutionary, and other dungeons do it, but I'd like to make sure it's a main descriptive theme.

I can have working traps and non-working traps.  I can have broken and rusted traps.  I can have poison traps where the poison has long since expired, though the party might not figure that out, if they spot the poison coating.

Ditto what I said above.

It seems like ideas abound. The challenge is to just keep them organized and spend some time getting them down in print.