You can use Column: Kind and File Type Group to get the grouping.
While you can only group by one thing, you could sort by extension within each group.
Groups will display a count of items in them, but if you want things like the total size of a group you'll need to select everything in it, which can be done by clicking the group's header. (If you don't see any group headers because the "Group" column is turned on instead, just remove the Group column and the headers will appear.)