Sir, I put all my bitcoins in the coinbase(KYC). Is it safe or dangerous for me?
This entirely depends on the person you ask. Many people are more than comfortable with holding hundreds of thousands in banks, and its the same way for exchanges. However, personally I can't recommend storing coins on something which you don't own the private keys too, and even if you can retrieve the private keys, you should be the only one to have seen them. This is just me, and some might argue that its being paranoid. However, if Coinbase was compromised there's a potential issue of losing your funds, if they haven't stored the coins correctly. Some exchanges make use of cold storage, but I can't say for sure with Coinbase.
I totally agree with what you said. Maybe I'm a little late. I would have benefited more if I had bought Bitcoin earlier. But I believe that Bitcoin will cross 50k in 2021. So I decided to hold Bitcoin.
I probably don't share your optimism so early on, but I do believe we'll be seeing Bitcoin cross the 50k mark eventually, not that it matters at that point. It all depends on the person, some people will be able to make more money by trading regularly, and reinvesting, some will do a mixture, and some people who doesn't want the risk of trading simply hold. It depends what your end goal is, and how much risk you're willing to take. Of course, holding does have a risk too, and trading might be less of a risk if Bitcoin wasn't to reach the aspired amount you want, but trading requires a little bit of skill, and a lot of luck.
, but then I might feel a bit of regret if that happens for not being able to learn trading at an early date. 
