$31000 per month, after tax (16%) you are left with $26000 per month.
you should be able to find an apartment 750-900sq/' 8000-10000 per month, add utilities, phone, t.v. which come to approx $2000 per month, you are left with say $14000. Subtract monthly food bill, 4000-5000 (2 people)and you have approx $9000. Subtract a little more for your monthly bus/MTR expenses, depends on where you live...
Budget for travel home, every now and then adds to the bill.
A big night out on the town or eating out will cost a bit though. Say $400-500 for two at an average restaurant. A boozey night $1000-2000 easy. Or the 7-11 drinking option at LKF, can reduce your alcohol bill.
So you will have a little cash to spare, not much, but enough to go to thailand for a few days on your days off with or without the Mrs. If you have kids at a school age (3yrs in HKG) then you will not have enough money. If you can get the Mrs working, that will be the only way for you to get ahead here. No housing in HKG makes it hard, but people do it, ask our CEPs. So you will be able to get by, but there wont be any savings and without your partner working it will be tight.
Hard to imagine, I lived on a lot less before. If you want a jet rating and can live without housing for say 5-6 years, then you can have a job where you can do a little travel, get a rating and move on to other things if it doesnt suit you.