Hi!
1. If you are reffering to product categories as results, then you can do that by adding them under the General Options -> Sources 2 panel.
2. You can do that via the taxonomy term filters – usually product attributes are taxonomies. Look for taxonomies with a pa_ prefix, like so: https://i.imgur.com/fqANZJk.png
3. I am seeing the correct font size (10px) according to the back-end. You have a minify/page cache active, the stylesheets are cached heavily. Make sure to always clear them, or turn it off until the configuration is finished, as the changes won’t reflect immediately.
4. You can either use the results shortcode, to place the results where you want them on the same page.
The results page grid may work as well, try enabling the live loader feature – it will then try to auto detect the results page and refresh the grid if possible.
