The crowdsale IPO refers to the public sale of the shares of the company, with the goal of collecting funds for development.
Initial coin offering ICO is also one of the fundraising methods the startups creating and selling tokens to raise funds for development. ICO refers to pre-sale and public sale. ICOs are related to blockchain technology.
Both ICO and ...
You are using MintedCrowdsale which requires for the crowdsale to have mint permissions on the token contract.
If you do not want for the crowdsale to mint tokens you have to inherit from AllowanceCrowdsale.
What power or validity would the ERC-20 tokens entered in smart contracts have over this new network the tokens are to be exchanged for?
They do not.
ERC-20 serves as a tradeable interim token before the real protocol launches.
Conducting token sale using a smart contract only ensures the money is fairly and transparently collected.
Rate is explained in the OpenZeppelin Contracts Crowdsale documentation: https://docs.openzeppelin.com/contracts/2.x/crowdsales#crowdsale-rate
You can also ask questions about how to use OpenZeppelin Contracts in the Community Forum
Disclosure: I am the the Community Manager at OpenZeppelin