I use 2 addons for inventory management. I prefer addons with a single purpose. I'm not a fan of addons that try and accomplish 900 things.

The first is Bagnon, pretty simple, it's just a "all in one" bag addon - very small, does only what I want.

The second is Mr. Plow. It organizes your bags on the press of 1 button. You can add exceptions (for example, I like my harthstone, tabards, etc at the bottom). You can also tell it to ignore particular bags.

This won't help your "view other characters inventory" issue, but then again I tend to post first, read more thoroughly later and I ramble.