The third question depends on the second one. If Valeran is not there in the final debate and you have 0 PER, then you will miss out on at least 2 points. If Valeran is indeed present, then a score of 9 should be possible if you fulfill all other conditions (AWA 5, INT 5).
Oh, and the answer to your first question is: YES.
Fleeing from Valeran still should keep him alive for the ending scene, and in fact will be just equally impressed to see you there and offer his support.
It worked for me, I run away but still could get a happy ending. But it was long ago, not sure if that changed.
I see, thank you very much for your answers, I'll try it with Personality 0 (because I'm a greedy bastard) and running away from Valeran, and then I'll put it here if it works.
Thank you very much, I really love the game, I realized that there are many inaccessible areas that could be available in future updates, I hope that will be more content in the future, in fact I would not mind that it was in the form of DLC, I would gladly pay for the extra content.