On the "femslash" vs. "femmeslash" issue:
I don't care what you've seen on other people's LJs, or on fanfiction.net, or other fic archives, or wherever the heck you may have read the term "femmeslash." It is still wrong. This is not me being the high and mighty authority here--it's just fact. "Femme" does not mean "female," (at least not in a gayness kind of context) which is what "fem" is short for in this context. "Femme" has a very specific meaning in queer culture, which renders a term like "femmeslash" more than a little confusing, and usually inappropriate, and displays a certain level of ignorance--a level that makes queers like me look at your story and move on without a backward glance.
On "femslash" vs. "slash":
There is no "vs." here. Femslash is a kind of slash. Slash is a term encompassing same-sex relationships in fic regardless of whether they're m/m or f/f. The m/m equivalent of "femslash" is "menslash."
On "CharacterxCharacter" vs. "Character/Character"
The use of an "x" instead of a "/" comes from yaoi culture, not from slash. Please, if you're writing an anime/manga/etc. pairing, feel free to use "x" all you want, but there is a reason why slash is called slash. There are distinct differences between yaoi and slash, the primary one being that slash is NOT limited to PWP (plot, what plot?/porn without plot) fics, which is what "yaoi" means. So please don't mix them up.
Ad, um, yes, idolatrie has set a wonderful example, and I'm working on doing my own little (well, not so little) LJSlash manifesto now, myself! Whee!