If you don't have any experience at all, first ensure:

Car has auction sheet, grade 4 n above
Match mileage with auction sheet n current, current will be higher obv
Take an expert mechanic with you to ensure car is not accidented. Can also use pakwheels inspection service but it's now quite expensive. Ensure all working electronics, fine suspension, fine transmission by test driving, go over bad road to check suspension noises etc.
In pak unfortunately repaint of whole panels like a door o r trunk o r fender means it got hit at some point. But not always. Denter n mechanic will help you exclude a bad accident.
Must check error codes using a scanner.
In 19 lacs there are also other options but vitz is a nice car. Though not too powerful engine in terms of acceleration. Corolla is another robust alternative, but might not have safety features like airbags n ABS.

For any used car you have to get it thoroughly inspected. Most will also have reversed meter. But not an issue if car condition is excellent.

Plus 0w20 o r max 5w30 fully synthetic is the oil grades for vitz.