You got it right .. tho there is no need to even worry about Q-miles for the challenge! They are not applicable.

You may want to do a search .. EEEK . to double check when you start getting the Double miles bonus? Is it ON the flight that you make PLT-Lite or on the NEXT flight. Your calculation shows you expect it on the flight you MAKE PLT-Lite.

Also .. ex-LHR should you wish to use your new-found PLT-Lite status for access to the BA lounges when doing other OneWorld traveling . you need the new CARD! The Lounge Dragon there cannot (do not?) lookup you status online. There is a thread about lounge access for newly minted tiers .. get a printout from AA or some evidence for the BA ladies.