Let’s say, I have deployed an ERC20 contract to the main-net. Three days from now, I plan to deploy a crowdsale that inherits from this contract.

To create an interface, I need the contract address for the token & ofcourse, the solidity file.

Now, since, the contract is already deployed, I can get the address directly from etherscan, and since, I have the copy of the token.sol file, I can inherit the methods(read functions). Although, this token.sol file will only be an abstract contract(?), and does not have a migration file(?)