But is $4000 the high before the crash? Or will it go up to $6000 first? And when it crashes, will it go up again? Or is it just the start of a 6 month bear market?

Attempting to time the market will cause you to lose you money roughly 50% of the time.

If you believe Bitcoin is undervalued, buy it. If you think it is overvalued and you own some, sell it.