It's depend on you how much you need for trade, trade is free you can use of small amount to started.
and not recommended to using a lot of money if do not have a skill to do that.
Well if you are a newbie $200 is great amount to start for trading and when i was a newbie i also started with a small amount and i am so happy because i learn to trade really well and for me if you can bacame expert in trading if you will practice to trade everyday.