any amount is enough to put as a investment in bitcoin wherein amount of capital that you are sure after all it can give you good return , even not atleast one bitcoin because it a huge amount of money. 
And yes it's a good investment for future but just remember to invest what amount you can afford to lose so that no more worries and you can control your emotions when something bad happen in the market what i mean not when we you see a bad situation you will dump because it's a big mistakes..always think positive when you invest in it..