1) how much gold does the party get when they pick up a pile of gold in a dungeon?

2) what happens when the overlord goes through his overlord deck during a dungeon?

3) what happens to cards in the overlord's hand when the players finish a dungeon level?

thanks for any responses!

wellist said:

1) 400 in total goes to the party treasury

2) The OL gains 3CT. If he goes through his deck three times, the Heroes automatically flee the dungeon.

3) All threat and cards in the OL's hand, plus any cards in play (such as DOOM! or Evil Genius) stay in play between dungeon levels. Once the dungeon is done, its all discarded.

wellist said:

1) 400gp.
- There is no indication in RtL therefore the base rules stand unchanged

2) he gains 3CT (and shuffles the deck and continues).
- Whenever the heroes would lose CT the OL instead gains CT in RtL

3) Nothing. If the heroes are continuing on a later level then nothing is done to cards in hand, cards in discard, or cards undrawn, they continue unchanged*. If the heroes are not continuing then the dungeon ends and so the OL (dungeon) cards are all shuffled together (taking out any treachery and putting back in the cards Treachery was swapped in for, ready for the next dungeon.

*Note that if, and only if, you are packing up the game between levels, then there is a slightly different system intended to simplify the packing away and limit the required recording.
Also note that the fourth paragraph of 'Dungeon Level Setup' RtL pg 17 is in error and is only describing how to do the first level in each dungeon, not following levels. This has been clarified in the FAQ and may be the root of your question.
FAQ 1.4 pg 8
Dungeon Levels
The Dungeon Level Setup rules on page 17 are misleading. The Overlord should shuffle his deck and draw a new hand only at the start of the first dungeon level, not every level in a given dungeon.