Advancing from classical to rapid and then to blitz

How many classical games one should play before advancing to rapid time controls? Or you can play rapid or even blitz no matter how good you are at classical (though I think that would be a mistake)?

Is advancing to a different time control necessary?

If you enjoy playing classical more, the answer is: infinity.

If you don't mind every game ending due to the "who makes the last blunder" rule of < 2000 rating chess, the answer is: however many you choose.