If you're worried about putting sex in stories you should read Mark Arbour
There is a thread about it somewhere but, and I am sure that someone will let you know if I'm wrong, I think the consensus was that as long as there is a strong story and it's not gratuitous porn then it's pretty much okay. Sex between adults and minors is not liked but sex between minors, at least non explicit and graphic sex seems to be okay.
As for font and style that is a matter of taste and I would suggest you experiment in efiction. There is an option the preview your chapters before you post them.
To be able to post in efiction you need to be given author status. You just have to ask one of the admins... it is usually recommended that you email JSmith I think. There are details of all the contact details on the forum. You also need to register separately for efiction.
There are lots of things you can't do until you have made 5 posts on the forum and posting stories in efiction may well be one of them, I'm not sure.
When you start to post a story you need to rate it and you can put warnings in your story notes.
I think that's everything I can think of but if there's anything else I can do just shout.