I'll answer the simplest question first.
where to find the convert multi-object to button control?
It's called the Object States panel, and it converts objects to "multi-state objects." You should be able to look it up in InDesign help.
The problem is that this is useless for creating eBooks. The EPUB format does not support it nor any kind of animation.
While InDesign can export to EPUB in CS5.5, it cannot export to Kindle MOBI format. You have to use a converter software like KindleGen or Calibre to do the conversion. But Kindle's format is more brain-dead than EPUB and doesn't support some EPUB formatting.
It sounds like you need to learn more about eBooks. My first recommendation is Elizabeth Castro's "Formatting ebooks - EPUB Straight to the Point". Excellent introduction. You can also look at Anne-Marie Concepcion's videos on Lynda.com about creating EPUB and Kindle format from InDesign.
Yes, I had read the help file, plus an online walk-through, set it up using the Objects States Panel and 2 sample PNG's. Can't find any way to convert to a multi-state button which could have an action to advance from image 1 to image 2. I have a full CS5.5 Design Premium suite installed on a 64-bit Win 7 machine, and it seems like a good install when I use other suite programs. But, this action seems to be missing. Any other way to look for it? (I understand that it won't matter for a Kindle eBook, but I'd like to learn about this InDesign feature anyway, if possble.)
You need to have buttons separate from the multistate object to control moving through the slide show. See illustration below.
The multistate object slide show is shown on the left. Above it are two buttons. The right button is selected. In the Buttons panel, the button is set to have two appearances. The object slide show is selected ("Seeds Slide Show"). An action is set for the button ("Go to Next State"). The second button would use the action "Go to Previous State".