You can't avoid mountains but by using Interstate you will barely notice a change as they are built with gradual curves and gradients designed for the biggest of rigs and generally have safety rails. As for personal safety you should have no problems. Everywhere is someones home where they take kids to school etc and getting to the 'wrong part of town' is normally off the main path. Usual rule is, if someplace doesn't feel right it usually isn't so move on. Trust your gut feeling but I don't think it will be an issue. Safety issues are normally based around fatigue and speed on the road and although speed won't really be an issue for you, fatigue could be and it creeps up slowly and then slaps you right in the face. That is why I recommended an extra night even though your trip is a straight A to B journey, they will be long back to back days and as you said, you have no experience of long distance driving. It's a marathon and not a sprint so set your days out evenly and avoid pushing too hard at the start when you are fresh and excited to avoid 'burn out'.