Fixed amount vs. infinite coins
Fixed mount is dumb, because there will sooner or latter run out of coins. Infinite supply is solution. What matres is schedule that is set in stone before first block is mined and stay that way forever. So at any point we exactly know how many coins will be in existence at any time.
know that you can just add more digits to the Bitcoin in the future to divide it to smaller amounts then satoshi. "Runnin out of coins" isn't a thing.