Generally, you could trade any number of pairs. You could choose several major currency pairs and a few minor or exotic ones to diversify your trading portfolio and pursue more financial opportunities. You could also start trading with just one currency pair. However, in that case, you do not have the option to hedge. When you choose at least two currency pairs, you have more chances: one could move in the predicted direction while the other may not. Thus, you would still have some rewards. So, always consider the option of hedging while trading Forex.