It seems OK to me. Obviously you will have your BA App in full working order to get the return boarding pass, and if that doesn't work print at home or the LHR lounge. So long as you get the check in stage done then someone in LHR or SVG will be able to print the boarding pass, however. And of course you should go HBO all the way, but you were expecting that.

You'll have about 20 minutes seating by the gate, so unless you have some spare Krone, I'd get a bottle of drink from Pret (or whereever) before departure, you don't have a liquids problem on that sector and SVG airport refreshment is regarded as extortionate even by Norwegians. Also I wouldn't necessarily rush to get back onboard, they sometimes hold people on the gangway for a few minutes before on to the aircraft. But otherwise.....

I'm less constrained: bullet proof and idiot proof.