Hi,
For #1, #1.a,
you can follow the link below documentation,
Template Files
by default, you are using link-template-default.php
for link template and page-template-default.php
for the page template. As documentation, you have to copy the file in the theme directory naming a folder called download-manager, then paste it in tpls>page-templates
for page template or tpls>link-templates
for link template. And you have to replace [download_link]
with <a href="[download_url]" class="btn btn-primary" target="_blank">[link_label]</a>
in related php file
For #1.b please share your file URL,
For #2, you can update your description page of related file,
thanks
Thanks.