Here are the answers to your questions:
1) By default the gantt widget does not support this functionality, but it could be achieved with custom code. Here is a dojo snippet
showing how to achieve such behavior. Please note that first the task is inserted with default values and then the edit form is opened so the user could define the task fields.
2) You could subscribe to the edit
event which provides reference to the form container element and to attached an event handler to the "Save" button's click. This is also demonstrated in the above provided dojo snippet.
3) In order to customize the edit form a template
could be used.
4) You could use the same approach as the one used to attach an event handler to the save button. The edit event offers a reference to the task being edited.
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