For #1, no I don’t know of a way to add a stop to an individual slideshow.
For individual slide control you can use the Slideshow Aviapoly Slider and then on each individual image use the Aviapoly Options to control the effect for each image as it transitions. It isn’t the same as the slide in or fade slider, but its the only way to get individual control over each transition.
The Aviapoly solution works up to a point, but for the degree of flexibility and control I wanted I found CodeCanyon’s LayerSlider WP plugin is the answer. Works perfectly in Choices. $15 very well spent!