My assumption here is that they will head back to Otari to rest every day, but this could be a wrongful assumption on my end. When they still haven't gone into any of the floors, this is fine, but what happens when they have made it to the first level, second level, and so on? Do we just skip to them being at the, say, third level after a night's rest, or do we play through the previous levels again, now empty?
It's totally up to you of course. In my game, I did the following:
- With each new foray into the levels below Gauntlight, I described the route the party took and (roughly) how long it took them to get where they where. This helps to drive home the point that it is in fact a sprawling dungeon down there and that travelling to-and-from Otari becomes increasingly taxing as the party delves deeper.
- I used a small table of random encounters ('wandering monsters') and let the dice decide whether or not this would lead to an encounter as the party travels through the (cleared out) levels. This helps to keep the party on their toes and highlights how dangerous the Vaults are.
Sometimes its enough to just roll some dice in a menacing way, followed by a "everything seems to be okay" ;-)
I think you don't want the party to get complacent and overconfident, and make the dungeon feel 'alive' and dynamic.
I also did what Haydriel suggests. Here's the random encounter tables I made, for reference!
I wanted to incentivize use of the teleportation circles, so any floor that the party passes through on foot triggers a random encounter check. At one point, my players recruited the mitflits and allowed them to take over the 2nd floor, so I eliminated the random encounter checks on those floors.
The random encounters ended up not being much of an obstacle because my party found the secondary entrance on Floor 5 (through the smuggler cave), and activated a bunch of teleportation circles. They ended up going back to town to rest for most of the adventure, and only rested inside the dungeon one or two times!