@Anneysha7 The "guidelines" for fanfics are fairly loose. The main thing is that you should include a disclaimer acknowledging that you don't own the series and seek no profit from its use (take a look at the beginning of my stories for an example). Beyond that, go crazy with it. Have fun. If you need any ideas, just ask; I've had a few fanfic ideas for Conan that I will never get around to writing, so I would be thrilled to hand them over to someone who will give them the life they deserve (I've already posted one such idea in this forum).
If you're going to post pictures or artwork, I don't really know the guidelines for that, but I know it had its own forum. You could probably find the requisite guidelines there.
I'll be keeping my eyes open for stories from you. I always enjoy new fanfics. If you need a beta reader, I will happily volunteer. I'm pretty good with spelling, grammar, and punctuation, so I could help you clean those up. I also have watched/read the entire series, so I may be able to help with keeping people in character and keeping the feel of the story true to the series. If you're interested in having me beta for you, let me know and I'll send you my email address in a private message.
Other than that, just welcome to the community!