Their Occupations

That sounds about right, I always figured Ray had some kind of white-collar office job, so real estate seems like it would fit. Even though we don't know what Mark's and Art's jobs are, I think it definitely makes sense for them to be managers since they're always (or almost always) at home and never concerned with their jobs.

Ray's home all the time but he's on vacation, and Walter's old enough he could be retired. Then again, with how wealthy he apparently is Walter could even be a manager or company owner who can simply work at home or doesn't have to be involved in it.

I'm not sure how old Mark's supposed to be but considering he mentioned being in Southeast Asia and his night-scope, perhaps he was special forces of some kind and now he's retired as well. However, considering how military-oriented he is and how he seems to have all this military gear on hand I could also see him owning a military surplus store.

Can't be too careful with all those weirdos running around.

In the beginning of the movie, Ray references that one of the neighbors is an "arms dealer" - I assume he was referring to Rumsfield. In the same scene he also refers to another neighbor as "the crazy person" down the street. I don't know if he's talking about Walter or not. I don't think it was Art, as he lives right next door - not down the street.

Being that Art doesn't seem to be working I suspect he is maybe a teacher on summer break.

Rumsfield I agree with being an military supply store/gun shop owner. Also, obviously retired military.

Ray is an over worked white collar something. Accountant maybe? In the original cut of the movie it is revealed that he was actually laid off from his job, not on vacation.

I picture Art as a salesman of some sort, used cars maybe.