We can't meet all of your requests but I'll help where I can.
1. Open more than one cases at a time : we don't have this functionality but it should be achievable by right clicking and opening cases in a new browser tab.
2. Sort cases based on last update - this is possible by using the 'Search requests' bar. Note this is not the main search page but the search bar specific to the request. You can then sort cases by using the command - order_by:updated . We'll look into this and see if it is possible to turn the headers into links for more automated sorting by fields.
3. Name of the last person to comment on a case - this would require a major re-design, we'll discuss this but the earliest a feature like this would be available would be the next major upgrade to the support portal.