You can follow as many as you want to follow. However, it is not a contest to see how many you can follow.
Following should be for those you wish to read again because you have found their work informative, interesting or entertaining.
Those who go on "fanning sprees", adding as many people as possible in hopes that the favor will be returned, are often not highly thought of. It might lower your hubscore if you seem to be fanning excessievly with no particular reason. I have seen one hubber who fanned literally many hundreds of people, for several days in a row, with no other activity. He was banned at some point.
Following hundreds of people is not really helpful to you in itself.
Reading the work of others and making good comments is.