Redmine

I'm building an application in Java using MySQL database. There will be 3+MM rows of master data per year. I want to be able to attach emails, Word docs, spreadsheets, etc. to individual rows, preferable by browsing or dragging from a list to the row.

Within the app I then want to see a list of docs attached to each row, and then click on a doc to open it up.

Redmine was a recommended solution. Do you have an API that does this? If so, what are specs, requirements and cost?

Thank you