Still work in progress regarding the requirements for this part. How to make the best use of categories and keywords.
Most eCommerce has support for adding products to a category or collection, also nested within a sub-category/sub-collection.
The collection is in place, but to make use of the collection data available, we need to collect all collections and generate a collection "filtering" system.
This could be a Menu with top-level collections with sub-collections.
This could also be a Quick-filter system, along-side with the search field.
With dropdown menus.
For example where there is one dropdown menu collections containing all available root collections.
there could then create a "tag-cloud" with quickfilters of keywords for available keywords (no duplicates).