So after doing some research, it looks like I'll want to get a 7-day Travelcard from the Heathrow Tube Station because there's no advantage to getting it at a rail station for the 2-4-1 deal. Apparently, most if not all 2-4-1 deals expire by April and I won't be arriving until late May.
Now the question is, what do I ask for at the ticket window? Am I correct in asking this...
Put a 7-day travelcard on an Oyster card and tack on enough PAYG money to cover the Day 1 Heathrow to London, Day 8, Day 9, and the trip back to Heathrow.
Another question, can I order this exact situation online and have it sent to me before I go?