I haven't flow on any international itineraries with AS so can't comment there but in terms of domestic you'd find it similar to AA. You won't get Premium Class seats for free even as a OWE. They are available for a fee. This is in contrast with AA where you would get MCE seats. However, the next bank of seats should be available and labelled for OW Elites. You should wait until after your ticket has been issued to go back into the booking and then select your seats. You should get Group A boarding. Lounge access will be available irrespective of flight length but your BAEC number needs to be in the booking.

Equally, I haven't flown in Y for a while but I believe you should get a complimentary drink or chocolate as OWE. My wife and I used to get the chocolates in First too, and a special greeting as Emeralds but this was immediately after AS joined OW and it seems to have fallen by the wayside since.

One nice thing about AS is that you can also link separate bookings via the website.

As for upgrades, I have had none on AS and barely a handful on AA when flying as a BA Gold. For the avoidance of doubt, when flying in Y on AA or AS there's no expectation of an upgrade given that you can't get on the upgrade list and so any upgrade would be purely operational and not based on status.

Tier points and Avios post weekly, on Wednesdays.