Just depends on your investment capital. It is better not to invest a huge capital in a single coin. Rather, invest in more than one coin as it decreases the chances of loss and increase the profit returns as well. Most of the coins are just pump abd dump coins, so you should be careful about which coin to invest in. Do consider the coin's undergoing projects, market capital and also its latest statistics before investing in the coin of your choice. In my opinion, you can invest in 4-5 coins at a max at the same time.