We populate the DA fields on a Lead, and when you convert a lead, it looks like this information has disappeared, but it is accessible in reports.
When a Lead is converted into an opportunity, the Lead isn't individually accessible anymore - if you try to view the old Lead record, you'll just get a page in Salesforce that says "This Lead has been converted". But Salesforce has effectively 'attached' that Lead to the Opportunity, and you can run reports on it.
To run a report on your Leads and the Opportunities they were converted into, create a new report with the report type Leads with converted lead information.
This report will show your leads, and if any of those Leads became Opportunities, it will show the opportunity information as well.
To segment for Leads that became Successful, Closed Won opportunities, add a Filter for Won equals True.
Or, to segment for Leads that became Opportunities, you can create a filter for Opportunity ID does not equal [blank]. (note - don't write blank, just leave the field blank).
From here, you can make the report a Summary report, and filter for Lead Source, DA Campaign Name, DA Landed On, or whatever you prefer.
It's not necessary to map the Lead fields to the Opportunity to report on them, but some people like to see them as well when they look at an Opportunity. Other companies like to see this information on the Contact. Some like to map it to the Account, giving them the lifetime value of their customers against the Lead Source information. We at Daddy Analytics have purposely chosen not to map the fields so you had the option to map them to Opportunity, Contact, or Account.
Mapping the Lead Fields
To map the fields, create corresponding fields on the Account, Contact, or Opportunity object. Then, go to Setup, and Leads > Fields, and click the button Map Lead Fields. You can then map the fields from the Lead to the Object / Fields of your choice. This will only work for all Leads not yet converted - Leads that have already been converted, and their relevant converted Objects, will not be affected.