A good vanilla or chocolate milkshake is best, in my opinion. I prefer chocolate myself. No need for the m&m oreo caramel marshmallow whatever crazy option. If you’re doing that, just have the milkshake.
EDIT: and as for the temperature difference, well, that’s part of the beauty of it. Hot fries and cold ice cream. Works better than you think!
Nope.
https://en.wikipedia.org/wiki/Tongue_map