More Thoughts on Characters

OK... Here are somethings I know about what I want in my story.

1. I know that I want this to happen in a D&D style world.
2. I know that I want this story to be about 4 kids as they head out into the big world, but somehow get caught up in things and become "adventurers".
3. I know the classes that I want my adventurers to be are: sorcerer, cleric, ranger and fighter. I have yet to decide who is what and what gender each are.
4. I want a minimum of one character to be female, but I'm thinking of two, but I'm afraid that would be a little too expected.
5. I know that I want my kids to have a profession that they've been training in, that they can fall back on, or even possibly use once they are trained in their adventuring class.
6. I know that I want this story to primarily focus on the characters, not what they're doing. I want this to be a story of the kids growing up to be young adults, and maybe in later stories, to adults, parents and leaders.
7. I want this story to show that life isn't fair, but you have to at least try to make life what you want it to be. If you don't try to make the best of things, you probably will be miserable, no matter what material possesions you have or don't have.

Questions:

1. What rules system do I use from D&D? If I want a hope of even possibly publishing this, I'll probably need to use the 4.0 set of rules. If I'm not going to publish, it would be easier to write this using a system I know, 3.0.
2. What kinds of things can my guys do that won't just immediately kill them off? I'd actually like to kindof roll things out as they go, but instead of people "roleplaying" the characters, I'd be writing out their actions/reactions as they go... to a point. If the dice go too badly for them I'll interviene of course.
3. Once they get started, what will keep them adventuring once they get started?
4. Sorcerer will probably start realizing that he/she has "powers" shortly after they've hit puberty. How will they manage to "hide" their skills? How long will they have been able hide this? Maybe this character isn't quite "of age" to go on the journeymanship, but they are a brother/sister/cousin/neighbor or the other of one of the ones leaving, and there is a sorcerer or wizard in the first town that they are going to be staying at that might be able to train them.
5. Ranger - this could be male or female, but what would their skills or training be? Possibly a hunter for the townsfolk and also is training to cure the hides for leather and furs?
6. Cleric - This person would probably be a bit of a "hippie" type, believing in hug a tree, make love not war (unless it's an orc or something.) I was also thinking about this character having an addiction of some sort, possibly 'shrooms or some sort of "herbal". How would this hinder or possibly even help the group?
7. Fighter - This could be either sex as well, but I'm leaning towards a male for this one. Mainly because I want him to have a kind of relationship with one of the females, and he is a little bit over protective of her, and she ends up saving his rear.