If i'm not wrong, Sabah/Sarawak residents are allowed to withdraw the entirety of CPF if you decide to leave Singapore. So, you can easily accumulate such amount as long as you don't splurge.

You don't need to change all at once. Can always slowly change and keep under your pillow!
It depends. My cousin just got a job in Singapore but have to take up any job though...even though it doesn't pay well. end of the day, it's all luck and perseverance. You're ultimately competing with other nationalities.