Questions about building a multi-client web app'

[eluser]InsiteFX[/eluser]
For the form handling you may want to extend the form_validation class and add your stuff in there.

For a multi-client, I would have seperate tables in the database for each client. Which you could load by client_id

Thats how Wordpress multi-user works, each user has their own tables for that user information.

InsiteFX