Hi Omid,
If I understand you right, the answers are yes, yes and yes (the first two without coding, the 3rd requires coding).
First of all, the Author permissions means that only the user who has written a value in the DB can also modify it (only that user and the site admin). This means that you can have values that a user writes (email, phone, links to uploaded files) that only he or she can see, modify or delete.
If the page with those controls is also marked as a site members protected page, you get the behavior you asked for in #1 and #2.
As for the follow up - Wix Database allows to store values that are “out of schema” - that is, any json value can be stored as javascript members of the stored item. This will require some coding to create a UI for custom fields and the logic to read it and store it in the DB. Data binding (a Dataset) does not support this idea and only support declared fields, so again you will have to code the data reading and writing using the wix-data APIs.