well the question was the MINIMUM amount to start
minimum is 10.000 satoshi,but if you want to make it more exciting I'd say deposit 0.1 btc
70$ should be enough to get some profit if you are successful and don't regret losing it
after all experience is the thing that we get when we don't get what we want
also I think that this is a normal amount for the start of trading. But only if you are not afraid to lose it. Do not try to make a lot. Be careful deliberation