Q1: I don't think CX will eliminate regional F altogether. But at the moment there is no guarantee that there will be F on your routes. They seem to turn F on and off with very short notice.

Q2: Maybe yes, maybe no. It might also be that the economy has picked up and that there will be no A availability all together. But many people had their A waitlists cleared in the past.

Q3: Yes, you can change carriers free of charge as long as the routing stays the same. Routing change costs $125 plus taxes etc.

Q4: No, stick to BA. You are aware that this itinerary is not maximizing mileage?

Q5: Your FFP membership will have nothing to do with the price. Normally, if you ticket a flight in one country but start from another, the higher of the two prices will be charged. However, for tickets sold in Canada the lower price will be charged. Canada is currently CAD 12,330 and US currently USD 11,250.

Q6: No, the taxes and surcharges depend more on the issuing carrier than on who operates the flight. So this is why ticketing through AA is much cheaper than ticketing through BA for example.