So could you technically apply "ile" instead of (y)le to any noun like "Benim ile"?
Every noun except pronouns. You cannot say "benim ile". Those are always contracted.
But you can say: John ile or John'la, for example.
Is this a sentence? I don't see a verb?
No, it's not a complete sentence, but easily the answer to a question like "Who should I go with?".
However, a Turkish sentence does not necessarily contain a verb.
Is it also possible to say/write Duo'le?
ile becomes "[y]le" when used as a suffix.
The "y" is necessary if the word ends in a vowel.
And since it's a suffix now, you also have to harmonize it: Duo'yla.
I have a problem with stress. Where should benimle be stressed? BENimle, benIMle or benimLE ? Not enough info on that.
It would be "benİMle" :)
Again I can see no difference if you put With Duo or with me - but marked as wrong
"Come with me or Duo" should be accepted. spoken more easily than adding another redundant "with". kinda disappointed.