The 4 types of release within Freshservice are Minor,Standard,Major and Emergency
Yes, we would be able to associate more than one change to a release from the release ticket.
No it is not possible for a requester to view the release ticket. It is only for agents.
Using analytics you would be able to create a report/widget for release tickets. Navigate to Analytics and you can choose to create a new report and add widget from the list of widgets for release.
Yes, if you navigate to Admin-->General Settings-->Form Fields and click on the Release tab you would be able to create custom fields for Release form.