I need more than custom 5 product fields and allow them to edit with (customized) Admin GUI.
How or where to look? Thanks.
Maybe your best bet is to add your own DB table and link to it from one of the product custom fields. You could use one of the custom panels in the admin app to maintain the new table.
Another thing I've seen done is to increase the size of one of the fields and to make it store all of the data you need as an xml serialized object.