There is no best way, it depends 🙂 If there is something like "best way", I will just put that limit inside "Buy now" and "Sell now" blocks. But it depends.
You may want to limit your trades by number or by time, or mixed. For example, you can decide to put 1 new trade on every new candle - here you don't care how much trades you have. Or, you can decide to have certain number of trades, for example 1 at a time.
Try this;
No trade is runniung -> Condition -> Buy now