The 1st obvious problem as raised by your software is that SEA-SAN is not valid since it isn't operated by an OW carrier

(2) anyone can pay for the ticket, it doesn't have to be you

(7) I don't understand why you would want to given that you are crediting to AA. The only flights within NA of QF (afaik) are QF107/108 between LAX and JFK and the seasonal SFO-YVR. The QF107/8 pairing cannot be used unless flying to/from Australia on QF; the SFO-YVR run should be doable

(9) No, It must be issued by 1 June in order to get the 20 segment allowance

(12) it reduces the total cost of your trip by GBP80. If you actually want to visit UK, I wouldn't be letting that issue be the deciding factor. If you don't want to visit UK, then you are nicely avoiding the tax

(13) how is your crystal ball. The OWE books in D class ( with a few exceptions ). You can make changes on date/time easily as long as D classs is available; whether there will be availability on a specific flight I cannot say

Dave