Demos of addons, Low Search, Variables, etc.

Hi guys, it has been a while since I have been here. Lots new going on. Unfortunately I have been unable to find any video or demo of some of the best EE addons like Low Search, Variables etc. so I can understand what they do and how they can operate. Considering that these addons are not inexpensive, there would seem to be more of a need to get a better understanding of exactly what they do. Can someone point me to this - nothing on youtube.

My current project is to build a site that is a document repository. It’s like a university library that allows for an abstract to a document, an excerpt, ability to create taxonomies and custom fields and, very importantly, the ability to have a drilldown search. For example, if you go to Amazon you start off with nothing and then you can search with a text search. You can then select from various categories/taxonomies on the left sidebar to continue to filter out results until you find a small enough set to manage. Someone mentioned this is like Low Search.

Other requirements are embedding PDF documents (which will take the place of the text if we only have a PDF.) In addition we would need to somehow have a relationship between documents and translations, e.g. connect the English to Spanish to Italian version of these docs and make it easy for a user to go from one to the other. I am guessing that this would be accomplished by being able to have a field that we can relate to a doc that references the other docs by its document ID number.

So it would very much help if there was a good list of addons (I saw one at devotee which is very slow and limited) and some demo or ability to appreciate the nature of these addons. Thank you all for your assistance and look forward to working with EE again!