synchronization of data with external system

Hi everybody!

I'm currently working on a Drupal site which has to integrate with an existing legacy system. Every day, I receive from the legacy system CSV files containing information about users and some nodes. I must read those CSV and create/update users/nodes as needed. I cannot directly tap into the legacy database, I must use the CSV files.

I saw that there are various import module, but they all seem "one-shot" oriented. I wonder what would be the best way to do this? More precisely, I have two questions:
- Should I write a module that hooks on cron, or can I simply write a script that includes bootstrap and then does it stuff
- Should I use any of the existing import module, or simply read my CSV, create my users/nodes (if they don't already exist), and save them, all that inside a big transaction.

Any tips or ideas will help.

Thanks!