A housegirl, if treated right, can be such a help for your wife and can make life so much easier for her. They are mostly wonderful ladies who will become part of your family. We now have second and third generation house-girls working in our family in PNG and I call them fairy godmothers.
For the delivery of your baby your wife will probably be advised to return to Australia but there is nothing wrong with having the birth take place in one of the major centres. All of my children were born there and most of my grandchildren. If there is one thing PNG midwives can do ,it is deliver babies but sometimes there are concerns if there are any difficulties that arise.
You will love Tabubil so take advantage of the fact that your wife can have home-help and she may choose to perhaps take cooking lessons or something that she would have never be able to do when she has to work.
Education standards are not always the best but the international schools have to maintain the standards to keep open so as long as it is primary education you are ok.
You would be advised by friends you make as to expectations in the way of wages so don't rely too much on people who give quotes and offer to find staff for you.Especially if they are males.
Don't take someone from the city for several reasons 1.If they don't work out they are displaced 2.You would probably find it hard to get them accommodation 3There are lots of housegirls already trained floating around in Tabubil who live with their own families and wont need accommodation.
Good luck!