To increase the number, you can modify the file
template-portfolio-4c-sorted-full-width.php. You can modify the
posts_per_page argument at line number 19.
You have the option to paginate too if you use the page template ‘Portfolio 4 Column’ but does not come with filtering due to small number of items that are displayed. Due to technical limitations, it’s not possible at present to have both filtering as well as pagination in the same page. Hope this works for you.