Proper use of .call and .delegateCall - In line 22 within my withdraw function, I opted to use call instead of transfer as suggested within the course due to the Istanbul hardfork. As gas costs are not constant, and transfer uses a hardcoded gas amount, it should be avoided going forward. This does carry an added risk of reentrancy, but because I have made the withdraw function as accessible only to the owner of the contract, I don't believe there will be any issues.
Pull Over Push - I prioritized pull over push in my mintNFT method. Instead of allowing for multiple possible mints and taking as an input a number of tokens to mint - which poses other gas related issues as well, I structured my minting function to only mint one NFT at a time. There are some gas tradeoffs with this method that are negative that I will look further into in the future.