ESF schools are cheaper for starters, tho recently they have been losing alot of credibility due to subsidy reductions from the government. I would say it depends where you intend your children to go to university - ie. as in which country.. if the US, then HKIS would probably be your best bet, if UK then and ESF school and well if australia then it doesnt really matter
Any school you choose will have decent enough facilities for all the sports you mentioned. You will find that alot of them dont have the facilities on site and the school will arrange transport to the nessacery places. - this is mainly due to hong kongs lack of space, or should i say expense of space!
On the location to live part of your questioning clear water bay is a really nice place and will probably suit you coming from NZ than alot of other places! It takes around 1 hour to commute to central from there bus + mtr (underground). Or if by car say 30-40 mins max. You will also get alot more for your money out in a place like that.. As said by someone in a previous post dogs are not allowed on any beaches so moving somewhere like clearwater bay that is basically one big park would again probably be ideal for the likes of a dog
Any other questions just shoot!