I am here now so can answer my own query.

Lounge is not crowded, but not dead. Those who are here talk loudly and there's lots of clanking dish ware, etc so sleep isn't going to be easy. There is one little room to the right, after you enter, that is semi private and seems to offer the best chance of catching some shut eye. The lounge itself isn't too great, but its open all night, has a modest liquor selection, some sad looking hot and cold food options, and will give you free wifi via a code.

When the Aadmirals Club opens at 4:30am we are moving over there.

Oh and though we were prepared for the worst due to what others have said, we cleared immigration in 5 minutes, and had our boarding passes and were back secure side within 15 total. Guess we were lucky!