While in Track view, right click the column name area. Now click "Set Displayed Fields". Scroll under "Other Fields" until you find "Publisher" now move it over to "Selected fields".
As for seeing the amount, all you need to do is highlight once you've sorted by publisher. Musicbee automatically shows all data for highlighted items at the bottom right (amount of songs for track view, amount of albums for album view, as well as file sizes, queued etc.)
If you don't highlight, then it'll show the data for everything in the current tab.
Here's a screenshot