Assuming the planets orbit is in the Goldilocks zone (the distance from the star where the temperature is just right), if the orbit was too irregular or elliptical, the planet would fly out too far to where it is too cold to maintain life and sustain liquid water, and the planet would fly too close to the star making it too hot and unable to support life.
No, The law of conservation of matter states that the mass of something cannot change if nothing is added or removed.