There is no limit on the number of records in the application. Output is possible within Salesforce limits, such as governor limits.
Salesforce Subquery Limitations
If the template contains Long Text Area/Rich Text Area merge fields of the child object, the maximum number of child records is approximately 50-200 records.
Approximate maximum number of child records
The approximate maximum number of child records verified in the sample template output is 480 records. The maximum number of child records varies depending on the template, record values, and number of fields, so check with your template and output content in the Sandbox. Maximum number of child records (Sample template: Word)
Number of Child Record
Results
480 records
Success
490 records
Heap size governor limit errors occurred.
Instruction manual