I want to make possible for the user to SORT Apache Solr results based on some taxonomy terms.How can I do that? I also want to make possible for a user to change the number of the results on the page. How can I achieve both of them? Thanks in advance
I good way to utilize Solr for search with Drupal, is to use the Search API, is has a Solr integration module, which will allow you to setup a View with exposed filters and full text search. With the flexibility of Views, you should be able to setup the view to allow the users to sort as they wish.
I guess this comes too late for you but maybe will help someone else:
(1) Sorting can be handled with Facets: Facet API ( facetapi )
(2) # of results per page sounds like a Drupal configuration thing, maybe handled in the configuration of the Block in which you show the search results