the question is quite simple (but I did not find a clear answer yet online):
If I have only the licence for "AEM sites 6.3", what "form" functionalities can I use in production without buying the "AEM forms" licence?
the only ones that don't need the "Add-on feature / AEM forms package" (see screenshot - area 1)
Nothing from this list (see screenshot - list 2)
If the right answer is 2, are there any alternatives to manage and customize forms (something like a multi-field that let me build a form from basic elements like input, button, textarea, selects, radio...)?
The query has been asked previously also on the forums. If you want to use forms and leverage it's capabilities in production you need to have the forms License. Without forms add-on, you will miss major of the forms designing functionalities.