Both "I hope I'm not asking for too much" and, "I hope I'm not asking too much" are not wrong, but the second one is just a more natural way to ask, and is what I generally say. As for similar expressions, the only thing that comes to mind is something like, "If it's too much trouble, I understand" since it also shows that you don't want to burden them. I hope this helps! :)

Oh the ' Is it' is the question, but I typed a full-stop instead of a question mark :s Thanks a lot for your answer!

Well firstly the "Is it" isn't necessary. With the "is it" out, either way is fine.