Special champagne off menu for J? Never heard of it. Champagne in J is average. Nothing worth getting hammered on.

The TWG tea onboard is really nice. Try multiple flavor.

EWR - You can use BA lounge or if you're more keen and have time, drop the bags off and go to the much nicer Polaris lounge in a different terminal. You will need to backtrack for your flight.

I'm personally not a fan that flight. Unless you're obsessed with non-stop flights, you will realize it's way too long to be confined inside the seat. JFK-FRA-SIN is much more pleasant. The non-stop ones are something you do it one for cred of being the longest flight in the world. There really is nothing else special about it.