Answer (or my best attempt at a answer) for #1.
Wood is made up of cells that are full of water when a tree is living. When A tree is cut for lumber, it is seasoned through a process called kiln drying which brings the moisture down to about 7% moisture content (in Michigan). Once dried, the wood will shrink and swell as the humidity / temp changes. Think of how a dry sponge reacts when it gets wet.
My thought, if the counter was in the box but not shrink wrapped it took on moisture while in the garage. When it came inside it released the moisture and shrunk.
Here is a good article: