The thief tool, which is extremely useful, can be found here: http://www.qhcf.net/thf.html

You don't mean edges- those are something different. Try "help thief paths". I think that will show you which path is associated with each guild. You can study any path without joining a guild, but you may have to travel further to practice (to a guild that doesn't require membership, if you aren't a member). There are also a variety of the core thief skills that you can study at any guild which are very useful, depending on your build.

You can mix and match, yes, but most of the best skills are later in the path and they must be studied in order (you can't skip ahead without studying the previous skill on that path), so you'll want to be careful about jumping between too many guilds and spreading yourself too thin. It's probably best to pick 1-2 paths to focus on, and as a general rule try to get to the end of at least one path.