Could we have a checkbox on each of the emails and a "delete selected" button so we can delete mulitple emails at once
No, sorry... you would need to search for the emails with the Search option, then use the delete all (for the resulting list).
I found an easy to delete multiple email in whatever folder you choose. For example: go to your email inbox, touch "menu", touch "delete", press and hold the trackball, touch "menu", and the "mark all" box appears. touch "mark all", then touch " delete". and they will all be deleted. You can then go to the "trash folder" and do the same procedure. Works on "sent" folder, too.