If I have money now, I would buy half of bitcoin because in next three months it will double the current price. This is real because it always occur this way after 5 years remember in 2011 and 2017 from the market charts and caps. And this year will break more even.
Buying cheap is the best formula. But what is cheap? I would say that buying right is the best formula. Your formula may work for you, but I do not think it is universally applicable. As it comes with a lot of anxiety. Besides, your idea of bitcoin's price is just a speculative as it is with every other person. Do not mount so much pressure on yourself because of FOMO. I don't know how long you have been in the market but if you have been here long enough you would have heard about Dollar Cost Average strategy which is actually the best out there. You should read up on it.
Buying right is the best formula, but what is buying right? I still don't understand what you mean. In my opinion, the best time to buy is whenever you have the money to buy, and the bitcoin price is still lower than the old ATH, especially if we are still in a bear market like now which is for the best. Buy cheap or buy low is what any investor wants, but how do you know the lowest price to buy? No one knows.
In my opinion, the best buying formula is to use DCA, using this strategy, we will never miss any low and will not regret whether the market goes up or down.