How much did Walter know before he joined the Men's Association...

Well after his first meeting he is sitting there drinking and he would stare in to space? Suspect that first meeting gave him a lot to process.

"It's the system, Lara. People will be different after the Revolution."

I think I remember seeing an "uncut" version several years ago with a scene where Walter later mentions that he had already struck up a relationship with Ted Van Sant while stile living in New York.

I watched it again last night since my first viewing years ago and noticed the same thing. In another scene with his wife, she is upset that he makes decisions without her and lists HIS decision to move and purchase a house in Stepford, CT. I also think he moved there with prior knowledge of the Men's Asscociation and their nefarious business, but probably was unaware of the details until after the first meeting. Plus, there is a weird scene with a cop and a Stepford wife in the road as the family drives up to their new home. The cop looks at them like he knows they are coming.
Ira Levine wrote both Rosemary's Baby and The Stepford Wives which is probably why Guy and Walter seemed so similar and quite callous towards their wives.
LOVE this movie!

The evening of the day they move in to Stepford, Walter goes to walk Fred and right at his driveway he sees Ted Van Sant across the road and says "She cooks as good as she looks" (about Mrs. Van Sant), in a way that makes it clear they've known each other for quite some time.

Walter knew exactly what goes on in Stepford before he moved there.

The reason he's extra moody the night Joanna finds him drinking alone is because he had just SEEN the process for the first time. before then, he'd only heard about it.

This movie has similarities to John Frankenheimer's "Seconds" (1966).

He knew that the wives of Stepford were encouraged to "change". But he didn't know the full extent of the program.

The night that he was crying in the dark, he got the full show. He hesitated. Yet he went on. Which means there was something more about the whole program that we never saw.

Which still makes me believe the wives aren't murdered but are brainwashed and conditioned to be whatever the Men's Association wants them to be.

It's "1984" redressed as a feminist horror movie. Love Big Brother or Housework is my highest purpose in life.

I've read the book and seen the movie many times. My take on it is he knows it's a good place to live and I don't think he knew exactly what happens to the wives. As many pointed out he seems shocked and troubled the night he is up late and sitting near the fire place. I get the feeling he feels regret but tempted.

I also agree the wives are clearly murdered and replaced with robots, not brainwashed or anything.