I live on a tropical island

but it's nothing like the one you're thinking of moving too!
WRT you questions though (because we moved from NZ originally and had to make all those decision too) ...
* what did you do with your house?? rent it out?? (we own).
We were renting before we moved but own two rental properties, we still own them but now have a property management co looking after them.
* did you keep your cars here or sell them??
We sold DH's car, defo wasn't worth holding onto as noone would have used it.
* what did you do with all your posessions??
We gave away and threw away a LOT of clothes. Sold major furniture that we didn't want to keep (some is stored at my Mum's farm). We kept a lot - stored with various family - and have since brought some other things back to Singapore with us and taken other things back to NZ (like winter clothes lol).
* what did you take over with you??
2 backpacks full of our clothes, treasured possesions and important documents. Also tennis racquets and sports shoes! I wish I'd take more underwear (impossible to get Fcup bras in Asia) and clothing meant for "western" women!
We were different in that we didn't have Callum before we moved. We've since done a couple of big moves within Asia too and when we moved to Singapore we (or rather DHs company) shipped EVERYTHING here for us and we bought a lot of new furniture when we got here as well.
Is there someone that you guys can be put in touch with who have been there done that where you're going? They will hopefully be able to give you real info about what sort of house to expect and whether it's worth bringing a lot with you from NZ.
My best friend here grew up in PNG, but she's in her 30s now so I guess things are probably pretty different

Or maybe not!
Just reread your post, if you were doing 8m on/4 off would you have to come back to NZ in between? I would maybe keep your house if that's the case although you'd probably want to let it out so mightn't be that easy to get it back for 4 months of the year? Do you have family that would put you up for that long? Or could you get some sort of allowance from the company to cover rental costs?
Lastly, if you think you can make it work DO IT. It's the most amazing experience living somewhere else for a while .... and if it doesn't work out, you can always come home