No, there is no limit on the number of orders you can create. But do note that if you placed multiple orders, the buying power will be temporarily be withheld in order for the order to be processed, even though it is not completed yet.

In some cases, if you have multiple pending orders, you might see your new completed order being charged a commission fee. That is because the system take in consideration the pending orders that has yet to be completed, into your monthly free trade quota.

If you cancel your pending order, the subsequent order for the month will not be charge a commission fee as your monthly free trade quota will be revert back accordingly.