Taxonomy views and relationship with events to get a range of dates

Hi.
I am building a website for an acting company. So it's basically about events.
Sometimes events are grouped, for example a festival or a bunch of events being performed in different places and dates, with a common topic. So to group the events i thought about taxonomy. And this is not a problem.
But i'd like to get from the events tagged in this taxonomy the information about dates.
Therefore i could handle these taxonomy terms to archive them or to get them out, for example, from the main menu when the last event has been performed.
First problem is when i try to get to define the taxonomy term page. When i get the date values using the relationship, i get duplicates, and i don't know how to get rid of them. To be more specific, i'd like to expose the first and the last date of all the events, in order to tell to visitors: this festival, starts on the day x and ends on the day y.
I just need a hint on how to get the right direction. Even pointing me to a tutorial, guide, or case history, would be really appreciated.

Thank you very much.
Alessandro