APT-Cache Policy – Understanding the Output

The sources.list file is actually several files: /etc/apt/sources.list, and files called something.list in the directory /etc/apt/sources.list.d.

This message tells you that you have duplicate entries in those files: you have several lines pointing to the same source. This is a warning: it isn't wrong per se, but it indicates that your configuration is probably not right. Look for lines starting with deb http://http.us.debian.org/debian wheezy in the files I mentioned above. You have multiple such lines containing contrib and non-free. Either remove the redundant lines or correct them if you meant for them to point to something else.

I don't understand why you are doing here. Why do you have a preferences setting for stable at all if you are running a stable system? As far I know, no preferences setting is necessary for stable in that case.

You don't explicitly say whether you are running a stable system (you really should say so), but if you are not, then I really have no idea what you are doing.

And if the release is on stable, then the usual thing to do for testing and unstable is to set their preferences to less than 100. I usually use 50.

And if you want to downgrade to stable, just do the following (assuming sane settings like the ones above) to downgrade pkgname1 and pkgname2:

apt-get install pkgname1/stable pkgname2/stable

This sets the specified packages to the target release stable.

Incidentally, mixing testing and/or unstable packages with an unstable system is generally a bad idea unless you know what you are doing. Some of the time it is Ok, but most of the time you need to use backports, either from Debian, or self-made.