I'm a sole breadwinner with 1 child. Is it feasible to buy car and let my wife be part timer GRAB driver as she doesn't want return to workforce and she wants to take care our child by herself?

If the main reason for purchasing the car is because you/your family needs it, then it might be viable for your wife to drive part time with Grab to earn additional income. But if it is so that she can use the car to drive for Grab part time, then it might not be very wise to do so. Reasons being you'll be clocking up quite a lot of milleage resulting in faster & higher wear and tear, thus higher maintenance and servicing costs. Driving on the road for long hours also results in fatigue and higher chance of getting into a road accident, touchwood. I'm following some groups on Facebook with PHV drivers inside and I understand that their earnings dipped quite a lot after Uber left the Singapore (SEA) market. In addition, drivers who lease cars from Grab preferred rental partners might have a higher chance of getting a ping/call/booking. Go-Jek is coming into the Singapore market soon so hopefully things will become better

Depends on your current income too. You can consider off peak car and hitch driver. Long term wise noticed you do not invest in stocks. You can consider a diversified ETF like STI ETF for a start.