I think Reeking_Revolutionary and I both have answered most of these questions for you to my satisfaction. I'll take another look at the helpfile later and see about clearing up some confusion if possible.

Just to reiterate, if your dual priorities are Freedom and Magic, it would stand to reason that you wouldn't use magic to enslave anyone, or you wouldn't use slaves to make magic. Everything else is fair game.

Your other questions:
1) Again, this is not a cabal with a strict philosophy and agenda beyond freedom and magic. You seem to have trouble wrapping your head around that. Disrupt social structure, free Magic... then, once these things are absolute, keep doing whatever you want, but in a more chaotic world. It's less nebulous than "bring the Eternal Night!" Being a loose-knit group of individuals, it's important that every Entropist has some individual goals or viewpoints, since it won't be satisfying to be a vanilla Entropist in the same way that it can to be a vanilla Imperial whose goal it is to just keep getting promoted. You've got to be yourself, together.

2) An Entropist *should* contribute a bit of uncertainty to CF. "I was going to go get darkened gear from the Mausoleum with my buddy, but Joe the Entropist just woke up. Do you think he's going to help us or kill us or disperse us? I have no idea." There's currently a character in-game who people really do speak about in this manner.

In theory, anyone in any cabal could login at any time to find Entropy has their item. In practice, Entropy doesn't really raid anyone but Battle -- which is fine and makes sense, given the magical focus of the cabal -- and sometimes Tribunal, which also makes some sense. Everyone generally just kind of floats around passively without actually doing much except fighting ragers and tribs sometimes. You could do so much more.

3) There's one around right now who is pretty well-known that I won't talk about until they're gone. It's the person mentioned in #2. There may have been one or two others but they were short-lived.

Finally, why don't you give it a try yourself? There's plenty of room to experiment, and wide latitude to make it whatever you want. Just avoid the Chaotic Stupid trap and you'll do great.