In regard to these issues, two things I noticed:
First, when you create attributes that will be used for variations, &/or whe all possible variations combinations are created...let's use Colors as an example...you will find that WC will create all of the various color potentials AND another one...ALL COLORS. If you leave that one, then clicking the color choices will not change the main image and the prices (regular and sales) will be what you set for All Colors, or the minimums from all the choices if you left All Colors price info blank.
Deleting All Colors, or the equivalent for some other attribute, from the product setup page's variations choices, will cause the images, price info, etc, to swamp on the product page when a different option is picked in the dropdown. Just what we want.
Second thing I noticed is that I can only cause the thumbnail gallery to be created when I first upload images...not from the media gallery. Something is strange. WC really needs to add a button to the gallery creation page to either add or delete the thumbnails, just as it allow images or the whole large gallery to be added to the post (in Product Details).
That choice should be given...to display all of the thumbnails, or only show the variations by selecting from the variations dropdown.