Are you planning on letting yourself go? Yes, after I get to know someone I feel less concerned with whether they are wearing makeup or have done up their hair, those things are the spice of life so don't overdo it. It becomes expected. Then you get negative attention for not being perfect all the time. Yes, looks take a back seat, the personality will become the future deciding factor.
No. Looks are crucial for first impressions, but it doesn't mean that it takes a backseat just because you get into a long-term relationship. Looks, along with confidence, kindness, honesty, respect is just one of the many factors that can affect a long term relationship. All are equally important