1) If you do not need the category tab, you can use the [show_post_snippets] shortcode for displaying the portfolio items on home page. Pls go through the documentation for this shortcode for more details.
2) If you do not need the details section, you can modify the single-portfolio.php file and remove the contents that populate the same (pls remove line numbers 49 to 94). It should be fairly trivial change. Also, pls make sure you remove the class ninecol from the line number 30 in the file.