Sorry, you can't disable the new editor.
Dictation: press the mic button on the keyboard or at the bottom of the Edit menu. I don't see it as an option to add to the ribbon. It seems like the first time you use dictation in a message, you need to use the keyboard, then the Edit menu works to reenable it if you disable it by typing.
Spelling - single click on the misspelled word. You don't need to select the entire word - just click anywhere in it.
When you are in word, your personal library of correct spellings works?