Send form entries to multiple databases

Gravity Forms does not save data to an external database. It only saves the form entry data to the Gravity Forms database tables in your WordPress database.

If you need to store data from the form in an external database you would have to do so by writing a customization using custom PHP and available hooks/filters. All of the Gravity Forms API hooks and filters are documented in the developer documentation area of the support site here:

http://www.gravityhelp.com/documentation/page/Developer_Docs

The hook you would most likely use for what you describe would be the gform_pre_submission hook or the gform_after_submission hook depending on when you want your code to execute. Those hooks will have access to the form data and then you can use custom code to put that data where you want it to go.

The field id's are dynamic and are created when a field is added to a form. They are unique to each form and are not customizable. But the field id's aren't important for what you want to do because if you are using custom code to send the data to a 3rd party... you have full control of how that happens. The hooks above have access to the form object or the entry object (depending on which hook you use) containing the data, you would then write custom PHP to do whatever it is you need to do with that data.

Any custom code you write using these hooks would go either in your themes functions.php or you could create your own custom WordPress plugin that you then activate to house this customization.