Delta uses Heathrow terminal T4.
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
Numerous airlines fly from Heathrow to Austrailia, from different terminals.
T5.
4x daily between Hong Kong and london/Heathrow.
Delta fly in and out of Terminal 4 at London Heathrow. See related link for more information.
Yes, there are three stations: Heathrow Terminal's 1,2 &3; Heathrow Terminal 4 and Heathrow Terminal 5. They are all situated on the Piccadilly Line.
Terminal 7
Heathrow Terminal 5 is on M 25 motorway.
Terminal 5.
About 20 minutes.