Basically, there are several methods for trading Bitcoin, as is often done by many crypto users, for example: spot trading, Margin, Futures, these three methods are often used by most users, As far as I know, these three methods are carried out based on the current price of Bitcoin and so on, you could say it depends on the market situation.

So, it's hard to say the first Bitcoin price to trade, maybe I don't remember what price I started from, but overall I did it when Bitcoin was going down, It's up to you what the price is, but stick to market guidelines, charts, analysis, volume and so on.