SQ economy is pretty decent. Try the Singapore Sling cocktail on board.

Use the business check-in and ask about bulkhead/exit seats on check-in, as if you have Gold they will often put you in these seats free of charge at the airport. They will also sometimes block the seat next to you if it is a low load flight.

SQ priority Boarding is a bit hit and miss and not always signed for Golds in Y. In practice just use the business class queue unless there is a signed queue for Star Gold that is separate the the economy queue.

I've not flown from BNE on SQ so not sure of your lounge options but the KrisFlyer lounges at SQ outstations are normally pretty good. In SIN you use the Krisflyer Gold lounge which is not great but not terrible either. it has no toilets or showers so if you want a shower and have Priority Pass/Lounge Key you might be better off with a third party contract lounge (there are several at SIN).