Your DBA will want as much information as possible about your applications data storage requirements. What are typical sizes for XML being saved, how many documents you expect to be saving monthly and how frequent updates are being made. This information will help ensure the drives for the databases are sufficiently sized. And if you have lots of users with frequent updates, transaction logs at short intervals will be warranted. DBXL also has a document history option, so each update could add to the storage requirement. If you will be using document history, make sure your DBA is aware of document sizes and expected number of updates per document.
Let your DBA know that DBXL v2.6 utilizes the SQL Server CLR. It is best to set a max memory limit on the SQL Server instance to prevent consuming all system memory. While SQL Server should relinquish memory back to the OS if requested, there are situations where SQL Server does not heed these requests.
DBXL also utilizes XML indexes to enable reporting and fast querying based on form's xml content without first requiring shredding to database tables. This functionality comes with a storage cost, which can be 50% or more of the content being stored. Starting with basic calculations of storage needs, your DBA can just increase the estimated storage needs.