Delta uses Heathrow terminal T4.
delta terminal
Delta fly in and out of Terminal 4 at London Heathrow. See related link for more information.
Numerous airlines fly from Heathrow to Austrailia, from different terminals.
Delta fly out of Terminal 2E in CdG Paris France.
T3.
There are various places you can fly to from Heathrow Terminal 3 such as Chicago USA, Amman, Oslo and Vancouver Canada. It is an International terminal that help you in your travel destination.
Yes
T5.
No they do not.
Terminal 3
west 2 east
You may not have the choice, only certain airlines fly in to Gatwick.
American Airlines, Delta, Northwest, and United.