Too many questions at a time..

Only FAQ/ Guide/ Digest can answer all of these... Just kidding... you may wait for one as mentioned above. Meanwhile, just to have my own opinon on couple of them.
(1) Trans cost depends on where you live and where you work... considering most remore scenario and assuming you take subway root, it should be somewhere HK$1000/ month. Usually less than that..... Public transport is fairly efficient in HK... For most cases you dont need car although having one is a matter of personal choice...
(2) Your whole family would be eligible for Govt medical services at nominal charge (HK$ 100 per visit) and their service is good, if not excellent. However, in certain non-emergency situations you may have to wait long and might opt to go for private doc, which is expensive... Most expats prefer to have medical insurance for that reason, i guess....
(3) For apartment selection, you may search all related threads on this website. Im sure you will get enough confidence how to go for it..
(4) Normally you have to pay tax at US as well as HK but for specific scenario you may consult legal expert...
(5) Food cost varies according to your selection especially for outside.. But, be assured, over all you wont find it expensive even at home.
(6) This is going to be a mega cost for you. There are subsidised daycare centers run by Trust/ other non-profit organization and they are good but frankly speaking i hardly see any expat child over there... You may go for private options especially those run by western groups.. The cost should range anything between HK$3000- HK$5000 / month.