Re "well stacked", the way I heard was that it related to stack height rather than fanciness. Here along the Mississippi River, the river often sits between steep bluffs. Steamboats with tall stacks could catch more breeze / draft and so could be fired more easily. Same reason why chimneys on a house are normally built to be at least a bit higher than the roof peak, better draft.
BTW steamboats generally had a pair of smokestacks side-by-side, one on the port side and one on the starboard. This perhaps explains how the term "she's well stacked" came to be transmuted from steamboats into a reference to shapely young ladies.
