So how to calculate the Max Supply? For example I see BTC has 21,000,000. How be sure mine will be 65,000,000? I use 50 coins per block with halving every 4 years like bitcoin does
It is calculated with maths.
For example, if you have a block subsidy of 10 coins, and you reduce it by 1 coin every block, then you will have a total supply of:
10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 44 coins.
How frequent are your blocks?
What is your starting subsidy?
When do you reduce the subsidy?
How much do you reduce it by?
And the most important question...
Why are you creating a coin if you don't know what you are doing? That sounds like a really good way to create something that is full of vulnerabilities and likely to be a complete disaster.