All the "auto complete" has is a data source, be it database or API, then a "text" and a "value" so.
- Have a database query to only look for the data to use for the Auto Complete which runs on page load possibly.
- Have a second database query that queries the users database where the extra info is stored that has a condition of the value of the auto complete
OR- Run a database insert/update with the condition set to the value of the Auto Complete chosen value.
To send the value from the auto complete to the server action use dynamic attributes on changed.
Here is a post I just answered with some of the stuff you will need.