The amount is should be according to how much that afford to loss. Good minimum to start is $100 to $500, by this amount you can growth your account trading by compound. And to to growth that amount is better to do trading in Metatrader so we can make profit from buy and also sell open potition.
Normally, anyone who is about to start trading should always not to be ready to lose, because that is not the essence of trading anyway. The reason why people lose is because they always refuse to learn, and even after learning so little, they are always in a haste to start making huge amount of money as the case may be which is the main reason why a lot of people get screwed in their first few years of trading, and eventually bail out if they get frustrated.