Hello!
1 - When you come through customs, you will then walk past your last chance to buy some duty free bargains. Then you will pass through a set of doors to be met by a long sweeping steel barrier which will direct you one way or the other... Follow which ever your heart desires...
You will see at either end, and set back, near the big glass wall of the terminal an elevator bank and a set of escalators. Each will take you to level 1, of which both will be sign posted for "British Airways Arrivals Lounge - By Invitation Only" and that will lead you to the bright blueness that will gain you entry to the sanctuary of the arrivals lounge.
2 - As the above states.
3 - Can't help with that one for sure, but I think it will be a no at T3...
Regards,