I have read dozens of threads saying you need to keep your BTC on a hardware wallet or paper. Anything online isn't safe they say. When trading that is not really feasible is it? I like to move in and out of positions several times a day and often at a moments notice. My trading account has a sizable balance (to me - 5 figures) in it.
How risky is this and any additional things I could do?
Trading is all about risk and you should not even go into it without proper knowledge of were and how you coin is going to be kept. we have many exchanger, that has reputable name and they have been in business for long that you can comfortably keep your coins. You should feel free in using any of the following exchanger: poloniex, c-cex, bittrex and livecoin.