How many smart contract addresses are associated with my ST20 token?

Your ST20 token will have ONE contract address, however your token may have multiple modules, each with their own address.

For example, an STO is a module attached to the ST20 Token. You could perform multiple raises using multiple STOs - Each STO would have its own smart contract address (each associated with their specific rate, hard-cap, etc...) without changing the underlying address of the token.