There should not be any limit to the size of the file that will be generated by the backup procedure. Well, actually there is, but it is configurable. And if necessary, the code can be modified to allow bigger files if the default max file size is not enough.
Here is an example with MySQL:
Code:
mysqldump -q --quick --user=your_db_user --password=your_password a2billing-1.3 -O max_allowed_packet=2048M > a2billing-1.3.sql
This will be able to handle a backup file of up to 2 Gigabytes.
Usually, you will simply go in the admin UI and click on backup. So far, I have not seen anyone needing to increase the size of the backup size limit, but it is possible. If you wish to delete you backups, then you can do it right from the Admin UI. I recommend burning them on a CD or DVD before removing them permanently from your server.
For the cards that have expired, I don't know any easier way than deleting them one by one. The other way would be to add some fields in the SEARCH CARDS form that can be used to search expired card and batch delete them.