JavaFXML ChoiceBox (ComboBox) and SQLite

I have created a ChoiceBox in scenebuilder and what I want is when the user clicks the drop down menu only the Firstnames from the customer table (SQlite) show. Allowing them to choose a name. I will add some code to show what I have tried below:

Another technical question. I would like the user to pick a firstname then continue adding more data in textfields. Once they have finished they will click a button which will add there entry to another database. I wanted to know do choiceboxes work like that? I.e. if they choose Ryan in the box then continue entering data like ID, number... (As an example) and once they click add booking would Ryan be added into that new database. Is that possible.

   private DConnection connection;
private ObservableList<BookingChoiceBoxData> custData;
String query = "SELECT Firstname FROM Customers";

private ChoiceBox choicebox;

public void fillBox() throws SQLException{
        Connection connection = DConnection.getConnection();
        this.custData = FXCollections.observableArrayList();
        ResultSet resSet = connection.createStatement().executeQuery(query);

        while({ //looping until last row in customer database
            this.custData.add(new BookingChoiceBoxData(resSet.getString(1)));   

    }catch(SQLException e){
        System.out.println("Error" + e);