You can adjust the padding and the font size to squeeze the accordion panel into a tighter place. Here is the style that you would want to adjust for this:
border-color:white -moz-use-text-color -moz-use-text-color;
border-style:solid none none;
border-width:1px 0 0;
font-size: 10px; /*these are the two extra properties that I added to make them smaller */
As for making the sub categories go vertical that would be a custom implementation of the accordion panel and would require hand coding to achieve. This is not a supported feature of PowerStore.