Tech trading is essential in keeping up with or staying ahead of the AIs; they also trade actively between one another.
Having the highest military rating helps tremendously in keeping the AIs from attacking you, so it's often best to have a decent military rating even if you want to play peacefully.
Knowing what score to expect is very hard as it depends so much on many of the initial settings, as well as how the game plays out. People keep pushing the barriers of what scores can be achieved, so there's always room for improvement.
Not sure whether it's possible to have a military victory without actually fighting, once the last civilization surrenders to you it might lead to an influence victory instead, I wouldn't know...