True there may be a smell among the place... but given these are a people that live within the semi confines of a cavern they may be use to the stench being a normal part of their lives. Think of it like living near a plant or an airport... after a time you will become accustom to these sounds/smells... if not you leave.
http://volcanoes.usg...s/gas/index.php
There is a great lack of volcanic eruptions within the caverns thus there is the potential that a great deal of the gases formed during eruption may not be present in lethal amounts. Were such lethal gases present at lava flows, I am most certain Lava Walking would not be permitted at all
I remember seeing a documentary on NatGeo about people traveling over volcanic planes... in fact I remember seeing them string a steak on a bit or wire and throw it into an open Lava flow that was barely an arms length away to cook it.
Orzammar is a very, very open area. True that Lava is not far from some area, there is still a great deal of openness that can ensure that a non-dwarf could be comfortable in these spaces... as comfortable as one can get being in a hot desert or a steam-house.
http://pubs.usgs.gov/fs/2000/fs152-00/
Issues from lava seem to come more from very hot steam from water suddenly boiling and sea water reactions with their salt content making Chloride... a partial component to acid. Thus forming a steam with a acidic nature.
Being that there are different caste, there may be an equal number of sub caste's. Smithing caste may be broken down potential to dedicated endeavors. Dagna does make mention of Lyrium Smithing, which in essence could be a specialized smithing caste. These surface warrior caste may be a specialized group of individuals.
Another thing may be that to a small degree so long as they remain on the steps they are still within the stones holdings.
As far as storage go... I can say from spelunking trips I have been on its really cold in a cave, especially the waters that flow in some recesses of a cave. For all intents they could have a section of caves carved out for cold storage of the more picky foods that may be off from the more temperamental areas. I know with some camping trips storing of food in a water tight container weight down under river/stream water can help keep foods cool as well.
Average Temps for some of the caves I have been in have been below 70 if not more going down, and some of that temp can change based on cavern size being that your body is going to heat that up.
Rotting today may not be like the rotting of things then... cooling something down can really make a difference in how long it takes to rot. Take for example a banana... peel, all black but yet the meat is still firm as ever. Anyways... just time and things are different... we are using chemicals and gene moding to improve the quality of the food and it does not mean that the foods of the past were not hearty in their own ways before we decided to breed out their natural growth.
But anyways just my thoughts on things...
Kudos for the Dwarf Studies... very nice.