I only trade with Eur / USD. Concentration in one pair is good for analysis. And I only trade long-term because I don't have a good strategy to follow. So, only this style that I follow. I can use several other pairs just to analyze and not to trade. and I think 2-3 years experience is enough to generate good profits. in a period of 2-3 years you learn more and more things about forex which has a direct effect on our profits.
I note that EUR / JPY and GBP / JPY move in the same way except that EUR / JPY is trying to catch up most of the time with GBP / JPY so I try to trade with the one behind. but by the way trading to many dangerous pairs is not recommended You will not know what to trade and which might lead to what you don't want and for strategy I only use one strategy, because I follow one strategy better than many strategies to followed, because consistency in developing strategies is very important. I use pairs for several main pairs, to analyze the market to the maximum. and use the M15 time frame to analyze
Before I tried a few pairs but as a result I was less concentrated but currently only 3 pairs I concentrated and the results were smart and the pair measured EUR / USD, GBP / USD AND AUD / USD. anyway some of my friends recommend me to trade gold and silver but i still don't exchange one exchange per pair and trading several currency pairs is more profitable, but for this we need to have more and more investments made in our account to maintain margins free enough. If not, we will be in deep trouble, instead I concentrate more on just one currency pair and I hope this will make me more profitable!