Seeing that te OP is departing in F, he has access to the F lounges. So by all means visit both the A concourse and the B concourse lounges. Depending on the time of day you are there, have one or two meals. I find the food in the lounges significantly better than on board, so don’t hold back! Don’t bother about the C concourse lounge, its hugely disappointing.

Never tried the massage myself, but in your case I would certainly book one. Do this early on as you may only get a slot a few hours later.

No gratuities, this is not the USA.