Hi @Proteu5,
Congratulations on deploying to mainnet! 
MAINNET!!
I want to create a tutorial for creating an art based ERC721 but haven’t come up with a simple way to create a JSON API. It would be great if you wanted to share what you did.
Feel free to ask all the questions that you need for verifying. The main issue I have found is ensuring you record what compiler version, optimization and EVM version was used to deploy the contract. A new issue is Solidity 0.6.8 introduces SPDX license identifiers and instead of flattening files, we will move to verifying multiple contract files.
I noticed in the screen shot of nft.sol that there isn’t any access control around mintUniqueTokenTo, so anyone can mint. I assume that is what you intended.
I am a big fan of auto token ID URI’s in the Preset to reduce gas cost. Though if you are including the IPFS hash in your tokenURI then this method isn’t for you.