when I'm in the contacts list and click the full name link of that person, said contact is displayed in the side bar.
Would I be able to configure that same side bar in the tickets view to get a quick glance of the history with that user?
Also, how can I add custom fields to either the side bar view or the full contacts view. I did try to edit views with the Forms Designer, but so far I didn't get further than creating a new view and not editing the existing one.
To add custom fields to the 'Tickets' list just add new columns as in a regular SharePoint list. Then, you will need to customise the ticket forms to add new columns to them. For that, you need to use Plumsail Forms for SharePoint Online. When you start it, connect to the HelpDesk site: