Well, my usual answer to this type of questions is invest whatever you can swallow or stomach to lose. I say that because when you are a newbie, it would almost be for certain that, sooner or later, you would experience a bump on the road that would give you a loss. Thus, if you have investment a fair enough amount that you would be okay to lose, then you would not face a situation when you would not want to keep going because what you have lost is too tough to recover from.