Hi Nick,
Hope you are well. For creating and cloning templates and for the full feature, you may have to use the PRO version of WPDM PRO, you shall get the features as I image attached for creating templates,

And for Free, it has a limited version. However, you can also edit link-template PHP files too, if you want to edit any pre-designed template you have to edit those directly editing PHP files at wp-content/plugins/download-manager/src/Package/views/link-templates dir files,
for making backup files, you have to follow this doc,
Template Files
Template tags will be found here,
https://www.wpdownloadmanager.com/doc/templates/template-tags/
please check
Thank you and regards