It entirely depends on your risk taking capability and on how much time you want to devote towards trading. It is very much possible to earn a decent income through trading. You can start with 0.1 bitcoin but try to gradually increase the amount to increase return. However, initially you will have to spend a lot of time monitoring the market dynamics and making offline predictions. Have an excel sheet and start marking your predictions offline based on the live market price. Once you see profits in your offline predictions, you can start with actual trading with money.

Do a little research about arbitraging. It is a fantastic method to earn good amount of income. However, arbitraging with bitcoin is not recommended because of long confirmation time. Instead try arbitraging with ETH because it offers near instant transactions speed.