IMO it would be foolish to include 2 new teams in a single season - better to stagger the introductions over 2 consecutive years. Less strain on the player market, more 'free' publicity such as the new team unveiling their coach, their first player signing, appointment of the first club captain first game, their first win, first loss, first derby game etc.
As to when? If a decision is made on at least one expansion team by June, introductory seasons of 2014/2015 would be possible, otherwise it will be 2015 and 2016.