Hmm... rummaging through my game collection, it turns out that the most recent version I have of the Underworld games are from the RPG Archives collection that Interplay released somewhere around 1997. Does anyone here know whether they're patched versions or not?
They must be. The patch came out in 92 or 93 and all subsequent compilations are patched.
Fun fact: I used the levitate spell to get the blueprints for the mad dwarf, then ended up using his flying potion to get around some hard to reach areas on the third floor
That's exactly what you're supposed to do. There are a few places accessible only by Fly or Levitate.
I also found the sword blade on level 3 by using a scroll that let me see secret doors, picked up on level 4. I was searching in the wrong spot, and would never have guessed it.
That's because you were not paying attention or missed on a clue. You are told somewhere about a secret door behind vines on the wall. The spot with the secret door is one small section of wall, in the area where you're told the blade is, and it is the ONLY section of wall in that entire area with vines on the wall. Granted it IS one of the more difficult hidden secrets to find, especially since the secret door won't appear on the map until you click on the vines to move them.
Someone mentioned the artifacts being the key to some of the puzzles, but I have the Taper of Sacrifice and the Standard of Honor but when I look at them I get short descriptions.
Don't worry about this for now, it'll become clear later on. Do notice that some of the artifacts can be used in place of normal items - the Taper as a light source, the Sword as a sword, and so on. One mechanics spoiler: the Sword is unbreakable. It's not as powerful as the best weapons you can find, but it's convenient to not have to worry about durability (and you save on some encumbrance).
I haven't found the four levers that allow me to get the Ring of Humility yet.
You'll get there, just keep exploring. You don't have to do everything on one level before moving to the next, and you will have to backtrack, but do try to get as much done as possible before moving to lvl 7 (don't worry if a few things are left unfinished though). And keep a save just before lvl 7, just in case.
find an old woman's lost love and get some metal for a wizard. I have no idea how to complete these tasks, however, as I am missing either secret doors or some such. I haven't even met the level 5 friendly compound yet.
The metal should be easy to get to from near the wizard himself IIRC (there's a teleporter). For the woman, as usual take notes and keep exploring. The lvl 5 friendly compound is directly at one of the stairs from lvl 4, so you probably entered from another side. You may want to find it sooner than later, for a couple of reasons (not essential ATM though).