I am interested in purchasing the Training the Retrieve Michael Ellis DVD. If I am not familiar with marker training, will I need to to buy 2 DVDs?

If you aren't familar with Michael's system at the bare minimum I would definitely recommend the video The Power of Training with Food first.

Not only do you need to be comfortable with the system, your dog needs to learn the cues, gestures and reward method you'll be using for communication. The retrieve is a multi-step exercise and we don't want there to be any question in the dog's mind about when he's right and when he's wrong. I also do not want my dog to think when he's wrong that there will be any fallout from making a mistake. I simply want him to have the desire to keep trying to be right. Our goal is to build a great desire to participate in the whole process before we start adding a slightly stressful lesson like the retrieve.

As for how much time, that's something that I can't really answer. It all depends on how well you grasp the exercises, your timing and your dog's motivation level, etc...

For me, I also want my dog to be playing tug well before starting any retrieve work.

The Power of Playing Tug 
Advanced Concept of Motivation

Cindy Rhodes