A few things...
1) Shop around before making the big purchase. And by that I mean -- talk to your friends, people on your server who are in the same position as you, et cetera. You will have a hard time getting a good start if you buy a charter and are the only person in the guild and need to recruit 10 / 25 (whatever size you're going for). Sounds like a 10 man guild is up your alley to begin with. If you're going to make a 10 man guild, I would try to find a core of at least 5 people first. At least one good tank, one good healer, and a few good DPS. Or a second healer / tank.
2) There's no reason NOT to start in ICC 10. ICC10 is very much doable in gear available from triumph emblems. If you are having to advertise "Looking for 5 more to start 10m raiding guild. Will be running ulduar 10", you're probably not going to get responses. It's the end of the xpac, and remember, interest in ICC will probably wain within 2 months or so. We're kind of at a "now or never" point (more like.. now or Cataclysm).
3) If you want to be a good raid leader, it boils down to knowledge. You need knowledge of the encounter and you need knowledge of all classes in the game (to know if people are the right spec, what abilities they should be using, which people to assign to what roles for any given raid encoutner). The more knowledge you come with ahead of time, the better. And of course, you won't necessarily have ALL that knowledge yourself (though the more you strive to, the better). You of course will need to rely on officers who can help you. i.e. I main tank / guild lead / raid lead and know most classes pretty well, but I know sometimes if there is a healing issue that I'm not 100% sure how to fix, I have an officer who is a healer who can handle the situation.
4) If you want to successfully launch a guild this late, you will need a good plan, and importantly, lots of structure. i.e. planned raid nights with contingency plans for failure. For a guild getting started, one helpful thing is to set your ICC night early in the week, and make it clear that if you cannot fill the raid yourself, you will lead a pug as your guild. And during the run, feel free to mention "If you guys enjoyed this, we are putting together a 10 man raiding guild and are currently in need of these classes:" kind of message. I've seen a lot of newly formed guilds find success by starting off leading pugs and recruiting that way.
I would type more, but I'm tired. Good luck!
"Sometimes attaining the deepest familiarity with a question is our best substitute for actually having the answer." -- Brian Greene.