Its not difficult at all. Write all you want :)

The only difficult part is when you need to edit the story XD That is it for me. I am lazy when it comes to that. The writing easily flows when you have a well thought out plot and posting it will definitely get you started on things. I would suggest starting with your main otp, it will help you with your writing.
If you ever need help, anyone is willing to help you out. I've gotten my readers' opinions on things through polls and blogs, so having a good amount of friends will always help on here :)

It's not difficult at all.
Write a story! I'm sure it will be amazing.
If you need any help with anything around the posting or whatever it is, just tell me, I'm here ^_^

it's not difficult at all to post your story on AFF... PM me when you're finished, I can led you through the process step by step if you want :)