Yes, forex beginners must start with small stocks like two or three stocks in a day. This way it is easier to make more money and manage money also.
Actually, this question is rather contraversial. Some of the traders think that it is important to focus on one or two positions and watch them during the whole trading session, monitoring each price change. At the same time, other traders think that it is better to diversify risk by entering various positions simultaneously. In this case, even if one of your positions would lead to losses, other profitable positions would help to end day with profit. But it is important to keep in mind that in case if these positions are not actually diversified (there is a corellation between them) they could move in one direction and lead to the same results. That is why there is no one solution that would fit all situations. So, each trader would have to make his own independent decision based on his trading style and the particular strategy utilized.
If you know what you are doing there won't be an issue if you diversify as much as you want. Just don't buy randomly and call it diversifying.