OP, wishing you all the very best on this flight! My only additional tip is Seat 10A on the A350-900 ULR is quite nice; I know there's concern that galley lights or noise will disrupt sleep, but I never find that to be the case - SQ gals and gents are fairly courteous, and if they are being a bit loud, kindly flag it to them and they'll tone down. The added bulkhead space to move your legs around is unreal!

Also big +1 to what commaspace mentioned - think it's nice to try the non-stop long flight from EWR or JFK to SIN, but after doing so once, I always stopover through Europe now (whether on SQ or another Star Alliance airline). It's really nice to have ~1.5 hours to stretch your legs, take a shower, and get freshened up for the next leg. Even in J, you will find the 18-19 hours make you a bit antsy by the end ... at least I did (after a meal, 8-9 hours of sleep, and a second meal, as there were still 4-5 hours left in the flight).