Total number would be anyone's guess, because you cannot be sure of the firm order but an educated guess would be a firm order of around 50-100 more over a span of several years.
This will keep changing according to market conditions. But from the look of the things the CAE-Indigo tie up is of long term.
This site is beneficial to see the delivery of A/C in the near future
IndiGo - Details and Fleet History - Planespotters.net Just Aviation
As you can see out of the 3 in queue 2 have their registrations in germany (D) that means they are nearing or at flight testing phase.