No idea about the service but there should be at least a little dinner served.
Any seats from rows 1-4 will be great, they are in 2-2-2 layout so great for a couple.
I believe the check-in open 3 hours before the departure time (it was the case when I did SIN-DPS).
Don't arrive too late as passports can be lengthy in DPS.
Lounge wise I found the Garuda one disappointing, T/G lounge was a tiny bit better in terms of food/drink offer.