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?
I suggest you make 2FA security on each account that has a lot of BTC, minimize the crimes that occur in the online world, if it installed 2FA I think it is safe.
This is not just even about 2 factor authentication. The thing is about leaving all your funds in a trading wallet. You have no control at all over your funds and if what happened to Mt. Gox and co, happens, you are at risk of loosing your funds with no apologies.
The best way is to get a hardware storage or at least a desktop wallet like exodus that gives you the chance to be in control of your funds. Only leave what you are trading with in your exchange wallet and never use it as a main storage for your assets.