Base Training ?

Hi There
Ive been doing some reading up about the concept of base training and how with an efficient base of easy riding in the endurance zone, it would be benefitial.

What i would like to know is what would be the recommended period for such a phase?
Can one still do the odd race during this phase?
And what about if your like me pretty hefty and live in a fairly hilly area, how does one go about keeping the heart rate down?

Thanx for any insight into this.

Rgds
D