Are interviwes necessary?

If it fits the story, yeah.
If not, still write it. Just don't put it in the story.
I still have a document I wrote that was pretty much a nonsequential fun story about how I invited all my character to a party at my house--celebrating making it half-way through the story.
Silly stuff like that can stay out. Once you're raking in the money and the people are begging for more, then you can go ahead and add it in for a "Special Xtreme Edition".

You know, take all their money. Suckers.

I used the interview device in the prologue to my second novel which is number two in a series. I felt I needed to bridge the action from the first story and inform the reader of certian facts. To accomplish this I had my hero in a therapist's office as they examined my hero's insomnia and the possible causes--those deriving from the first story. The interview technique worked well in this instance. In the final book of the series I intend using an interviews throughout to tell the story.

Michael Halfhill
"I could never be satisfied with just the approval of the critics, and, boy, I've certainly had to be satisfied without it." -Norman Rockwell