There is no required amount to start trading, so decision is yours. Never spend more than you can lose without unpleasant consequences. Then there wont be a reason to worry about. You will easily go through the ups and downs of the market with an opportunity to buy more coins. In spite of apparent simplicity, its easy to get lost. But dont panic. Only a cold math and detailed plan are your friends. So Its better to care about your trading skills, than about the amount.