My husband is also a writer, so I'm constantly bouncing ideas off of him throughout my researching and plotting phases. Usually by the time I'm writing, I don't say much about story changes. But once I start writing, no one looks at my work until I've edited it a few times on my own. Then my hubby sees it, I edit it again, and then I send it out to beta readers and my writers group.
I have found that if I ask for a lot of people's opinions throughout the entire process, ideas get muddied in my head and I have a hard time remembering why I had something the way I did, and then when I change it, suddenly 200 pages down the road, I remember why, and now I've got to go back and fix it all over again.
But I have found it helpful to bounce ideas off of one person's head that I trust and that knows my story pretty intimately.
As for proofreading, I have a copyeditor's eye, so my story is getting proofread every time I read through it. I also have my writers group to go through proofreading for me, which comes after the story's been written and edited several times.