Hi, my intention is to take the underground when I get in on Friday, then take the Paddington link back Tuesday morning because I have a morning flight, and am staying a closer to that station. So, I'd want a card for Friday through-Monday. Can I buy that at the airport?
You won't be able to buy them from Heathrow, but you will from the tube station there. Ask them what they think is best, they will tell you if its worth getting a visitors oyster card or paying for a travel card daily.
I dont know how much it costs to get a visitors oyster card, but i would go for that option, since your jounrney will always work out cheaper than an all day travel card.
The oyster system works by charging up a card with money (from the ticket office or online). When you get to the ticket barrers, put the oyster card up to the yellow circle with a card sign on it (next to where you insert the ticket) and the barrers will open. When you get off the tube, put your card over the yellow circle and the barrer will open. YOU MUST SWIPE YOUR CARD OR YOU WILL BE FINED, sorry just to emphasise.
An oyster card only works for tube (underground) networks, to get the train from paddington you have to buy a single to heathrow from the ticket office.
If you are going to use an 5 days and doing lots of trips on the tube maybe but £35 on you card.
The best thing you can do is ask the ticket office what is the best thing to do, they are usually very helpful. Sometimes they can talk quite quickly (and in a weird london accent) so just ask them to slow down and talk through your best options. Even talk to the guys manning the barrers if they arent to busy, they all know their stuff!
Hope you have a great trip in London!