I'd just like to clarify that the text files to be imported are on the server, not on the user's local machine. If they are on the user's local machine, you might run into sandbox issues.
the text files are owned by the users and they are downloaded on the server. The app then reads from there. Is that what you mean?
Do you know of any ready examples or templates to start out? Considering my level a template would be very helpful. Or is it something I should write from scratch?
you should first UPLOAD the text file to the server, read with any server script; and return the TEXT(STRINGS) in a required format to FLEX.
Or you can load text file into Flash(Flash Player 10 required), read binary data and send it to the server. Server side script(ASP, PHP, Coldfusion, etc.) reads and writes String into the database.
There is no need to keep actual .txt files on the server.