Hi!
1. The results width in block mode (when using the results shortcode) is always 100%, it will occupy the whole column width. The search width is also set to 100% by default. You can force the 100% widths for both the search here, and the results here.
2. That is unfortunately not possible, as the isotope script sets the items to an absolute position, where the padding does no effect whatsoever. The closest possible solution could be to add a right margin to each result element like so:
.item.asp_isotopic_item {
margin-right: 12px !important;
}