If you made 500$ on a trade with the 1000$, you would then transfer 250$ and trade now with 1250$.
This system sounds too utopian. I think very few people can earn 50 percent a week from their deposit.
The only way to earn so much is if you risk very much by trading assets which at the bottom of the coinmarketcap list. But this is so risky that you are much more likely to lose all your money instead of making a profit.
In this case, you will have no any mind about your exchange security, because the greatest danger will actually come not from the exchange, but from the very fact of buying such high-risk assets.