You can include your portion of page with plain Apache SSI directive instead of using SDI if you can't install it. It would be something like this in your html files <div class='whatever'> <!--#include virtual="${'/content/experience-fragments//whatever' @ selectors='nocache', extension='html'}" --...

You can use 'Content Reference' data type in content fragment model to link any kind of internal AEM resources in your content fragment instances. You can also limit those reference per mimetypes, images max width / height, etc..

This is because you need to configure your front-end pipeline directory into your frontend maven module. I guess you're repository root don't have the package.json with npm script called build, it should be inside a maven submodule. Change pipeline location to your front-end maven module and it will...