$NVIDIA(NVDA.US)$ They all say there is still room for decline, so should I sell it first, wait until it's as low as 180, and then buy it back?

Moving average (MA for short) is a method of statistical analysis to obtain a moving average by averaging prices over a certain period of time and connecting the average values over different periods of time. The moving average is one of the technical indicators used to observe price fluctuations. It can help investors confirm existing price trends, judge potential future price trends, and find signals that prices are about to reverse.
Here I have selected a stock as a reference.
  $Berkshire Hathaway-B(BRK.B.US)$ 
Here are my observations:
Here I used the 5-day, 60-day, and 250-day moving averages.
Decline signal
The red circle 2-moving average rises and then falls. When the short-term moving average falls below the long-term moving average, this is a signal to sell.
Red circle 4- There is a high possibility that the stock price will fall to the moving average after a sudden sharp rise in stock prices.
upward trend
Green circle 1 - the short-term moving average is above the long-term moving average
The decline in the green circle 3-average line gradually stabilizes. When the stock price is above the average line, this is an upward sign.
Green Circle 5 & 6- The stock price suddenly plummeted far below the moving average. The stock price deviated too much from the moving average, and there is a high possibility that the stock price will rebound.
Basically, stock prices are above the 250-day EMA, so you can buy them for long-term investments.
The support price of the moving average can be used as the price to buy or sell.
Technical indicators provide an important perspective in due diligence, but they aren't always 100% accurate.
Normally, it is difficult for investors to quickly and accurately determine the best entry by relying on moving averages alone...

$Coca-Cola(KO.US)$
are most trading on this stock? or holding it for its dividend in the long run?

$Tesla(TSLA.US)$ chief executive Elon Musk has sold around $5bn of shares in the electric carmaker.
The documents showed that the sale of about a fifth of the shares was made based on a pre-arranged trading plan set up in September. 14 , long before Mr Musk's social media posts at the weekend about selling some of his shares.
The company's shares fell by around 16% in the two days after the poll came out in favor of him selling shares, before regaining some ground on Wednesday.
If you don't know what happened. Go check out the Daily Poll few days before.
Source:
Elon Musk: Tesla boss sells $5bn of shares after Twitter poll