Firstly, once you go through customs there is a check in counter past the arrival area where you can check in for your domestic flight. As such you won't need to take your luggage over to T3. From there you can take a bus across to T3. If you've got so much time it might be worth taking a little trip into the city.

Anyways, the business lounge has showers. Food isn't that great but they do provide breakfast, then a bunch of other things during the day. They have free wifi and about 4 iMacs.

Hope that helps.