Page didn't do anything with her knowledge of Cobb's problems, any time she discovered another level. Going along with Cobb because he's a nut case to do nothing about it is definitely pointless. Who knows why the others thought she was there?
The originally planned inception dream would qualify as a seed planted in a dream. But Murphy knows that extraction is possible and takes it seriously enough to get anti-extraction training. When DiCaprio tells him in a dream he's being attacked, it would be alarming and memorable. If he's going to forget that, he's going to forget it all, including the idea.
But there is one thing confusing me, which is why he needs to give Saito a gun. I thought he needed to find Saito to help his mind survive the unconstructed dream state (how mystical yet drab that jargon is!)
Is this supposed to mean he did to Saito what he did to Moll? And that Saito will eventually go mad and kill himself?