It is the best option to trade only one pair of currency at a time. If you are a beginner, or even an intermediate, one currency pair at a time is the best option for you. This is because you will have to be constantly updated about the price charts as well as keep a track of the latest news that can affect the forex market in general, or your currency pair in specific.
If you are an advanced trader, it can depend upon you how many currency pairs you would like to trade at a time, as per your experience and skills.
If you are an advanced trader, it can depend upon you how many currency pairs you would like to trade at a time, as per your experience and skills.