If you buy it at 20000$ for sure its a big upset on you side because you loss more that 50% of your capital.
Can you Make an Advice When I should Buy Bitcoin?
And how much money should I invest on it?
Of course, everybody will be disappointed when looking at losses that exceed 50% of funds used, the last time when bitcoin prices have reached $10,000 and it didn't last long even within a week.
The last time I read an article from Pantera Capital, dropped bitcoin price since the beginning of 2018 was caused by taxation that forced sell a lot of bitcoin to meet the tax requirements. And They also explain that in 12 months bitcoin prices will be back at $20,000.
My suggestion is better to invest your money 50% of current price and wait within 12 months hopefully the article gives accurate news.