Warren,
Those are good questions, and also the same ones I had when starting to use a kiln. It is a bit confusing at first, and I will add that I don't know all there is to know about drying wood. I do know enough to satisfy myself though so that I am confident with what I am doing. With wood the drying process is critical to stability. The moisture content varies with different geographical locations. Wood on the pacific coast of CA will have a higher MC than wood in the mid-west, and so on, just because of the humidity found in that area. The humidity is higher in some places than others, as you well know, which will cause the wood to take on more moisture in some places than others (or lose some moisture depending on the location) once the finished piece reaches and is set up in it's new home. Be it one of my cabinets, or a piece of extremely high priced cherry furniture purchased from Thos. Moser Co., wood takes on and releases moisture for it's entire life even after being turned into something other than a simple board.
Anyway, a long reply getting a little longer
... I am happy with drying down to 6% in the de-humidification kiln. Some "experts" say 4-6% for dry climates and 6-9% for humid climates. The thing I see when looking at these numbers is that they both have 6% in common. It is a happy medium, or a place to start if you will. Air dried lumber may have a MC of about 10-12% to give you an idea of the difference between kiln and air drying.
All of the wood in the kiln is dried down to the same amount of MC. Different species will have different MC before going into the kiln though... some white oak may be 8-9% while some cotton wood boards could be twice that amount. I've cut quite a lot of cotton wood and you can see water run out of the wood once it is cut. Leave a large chunk sitting in a bucket, container, etc., and you will see water standing in the container within a very short time... cotton wood is very wet.
Now that the wood has been dried it will be stored in the work shop where it can acclimate to the area. This is because the shop is where it will be "worked" and made into something. It is stable and will remain stable although it will gain a little moisture and also lose a little with changes in the air. These changes will occur with the different seasons... dry here in the winter, and humid during the summer months. This is normal though and in no way makes the wood unstable. All wood does this, but remember mother nature changes things gradually which is why it is OK for the wood. Just like ivory that we have talked about in the past. Wood movement has always been there, and joinery always a concern for furniture to make sure it can move without causing problems. Kitchen/bath cabinets are made from veneer, The carcass is veneer, the back is usually a very thin piece of sheet goods like veneer, luan, hardboard, etc. Then the face frame and door are constructed of solid wood (actually the only solid wood on them). Even cabinets advertised as "solid wood" have a carcass made from veneer, it's just the industry standard I guess is a way to put it, and people just don't know it. They see "solid cherry" advertised on the cabinets set up on display and think it is solid... why wouldn't they, right? Veneer is actually a good way to make them. It is strong, and the exeption when talking about wood movement as it doesn't move. It is not affected by humidity changes and does not expand and contract like solid wood does. The pieces of the cabinet carcass are not seen anyway as they are installed next to each other and the only the fronts are seen and the veneer surface when looking inside (and an end of a row of cabinets if nothing beside it). If using the 3/4"x 4' x 8' sheet material in a matching wood veneer surface, it will work nicely for the life of the house in normal conditions. With furninture and having movement in mind (and we know wood will move) it's up to the craftsman to "build into" the piece when designing the joinery, a way for the wood to be able to expand and contract without splitting the finished piece apart. A table for example needs to have a way for the top to move, to shrink and expand, when the humidity changes with the different seasons. Today it is not as big of a problem as it was many years ago as we do have a fairly controlled climate with central air in most homes. You may remember many years ago though, it was common for a wood door on a farm house to close nicely in the winter when everything is extremely dry from fireplace heat, etc., and then not want to close at all (or rub a little) when closing it in August. Drawers would do the same thing... hard to open and close when humid, and work smoothly when dry in the winter. Wood can shrink about 1/4" of movement per 12" of width... that's a lot of changing going on within a piece of furniture when you think about a 4' table which could move as much as 1 full inch in width.
The best way to store lumber that I have found is to store it where it's going to be used that way you don't have to wait for it to acclimate before using it on a project. A separate storage building would certainly help a great deal with providing more floor space for machines, etc., but would mean having to bring the material needed for a project into the shop days ahead of time so it can sit and adjust before working it. It will fluctuate some while sitting there, just as it will in your home, as changes occur in it's surroundings. However, as mentioned, that is common and it will continue to fluctuate for it's entire life.
Hope this long winded reply helped...
~dale
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