Re: Conversion Tracking
In Google Analytics, you need to set up the Goals and Ecommerce Tracking to see how many users have converted using various traffic channels. If you haven't configured them currently, then there is no way to keep track of the old leads or conversions as per my understanding.
Read more on setting up goals here: https://support.google.com/analytics/answer/1032415?hl=en
and setting up Ecommerce Tracking here: https://support.google.com/analytics/answer/1009612?hl=en