Can anyone provide a high level overview on what are the issues that can occur while converting to Lightning for Knowledge and Reports/Dashboards?
I suggest going though these helpful salesforce links:-
Learn what to expect when using reports and dashboards in Lightning Experience. Some Salesforce data and features aren’t available in the new user interface. And some features don’t have full parity with what’s available in Salesforce Classic.
Enable Lightning Knowledge, create Knowledge record types, customize your record type page layouts, set access for Knowledge users, and create a Lightning Knowledge process.
Knowledge in Lightning Experience works differently than Knowledge in Salesforce Classic. Enabling Lightning Knowledge changes your org’s data model to use record types rather than article types. After you enable Lightning Knowledge, you can’t disable it. To move from Classic Knowledge to Lightning Knowledge, use the Lightning Knowledge Migration Tool. Before running the migration tool in your production org, test the migration in a recently refreshed full-copy sandbox. Verify all customizations and integrations to Knowledge. A carefully prepared migration plan minimizes the impact on production during migration.