You will not get AA FF miles on any BA flight between the USA and Heathrow. However you can get Alaska miles (25% of flown miles up to 150% depending on your fare class - 25% for most discounted coach tickets) for the BA segment, plus 500 miles for the EUG-SEA segment.

If it's all on one ticket, be sure they do a passport check at EUG, otherwise you may need to find somebody at the BA kiosk at SEA to be sure your boarding pass is in order.

I would hang out in the central terminal/food court rather than going to the South Satellite if I were you - much more to do, better views - and when you see the BA 747 land around 4:30, only then start making your way to the satellite.

I just wanted to update everyone on what happened. I found out BA could do a through ticket for me, since they are partners with Horizon/Alaska. I had to call BA several times to get an agent who knew that, though. She was in the process of booking me when the ticket price doubled! So I ended up going online and getting the lower price there, and was not able to do the through ticket (I couldn't add the Horizon flight after buyingt he BA one), but for someone else who is a little faster than me, that seems like the best option.

Thanks for the advice, Gardyloo. I don't think I will have the option to stay at the central terminal, because I wouldn't be able to get another wheelchair to the BA gate later. I could be wrong, but I'm pretty sure the deal with the wheelchairs is they just take you from one gate to the other.

It is good to know I could get Alaska miles if I want to! I'll have to think about which I am more likely to use.

In any case, I have my ticket now! Yay!