my wife and kids are here with me    .  wife is a housewife and kids primary school is just below the block  .... expenses is ok so far ... not really tough actually if you could manage it well

You can't import a used Malaysian car into Singapore.. actually you can, but you have to jump through a lot of rings and you'll end up paying a lot of taxes which you might as well put towards a new car.

You can drive a Malaysian car into Singapore but it will cost S$20 per day (there are a number of free days etc) but there is also a limit as to how many days the car can brought into Malaysia. The rules get more complicated if you have a long term pass (work permit or employment pass etc) where your car cannot stay in Singapore beyond a certain number of hours each day. Then if you have residency (PR or citizen), you cannot drive a foreign car altogether in Singapore.

Let me put it this way... if your current career level allows you to (comfortably) buy a BMW in Malaysia, then the potential new job in Singapore will allow you to do the same thing in Singapore. I wouldn't worry.