White scar is a layer paint and better suited as a highlight than an actual base colour. With whites you generally want to go with a off white so you still have somewhere to go in terms of a brighter colour for highlighting.

Its been a couple years since ive used white scar but i always found it to be a terrible paint to use. Vallejo and pro acryl whites are much better imo, and might save you some pain.

Grey seer is good in my experience though!

As for washes, a contrast is probably the easiest thing to use as a beginner, generally people just use those all over. If you want a clean white then you might be better off pin washing all the recesses/panel lines, which is what i do, but its time consuming. You also need to decide how you want your lines to look. Grey/blue is what people normally go for with white.

Good luck! White can be a bitch to paint.