First of all, you don't need to name your wallet files "WALLET"; You can name them "vanilla icecream.dat" and they will be recoverable in the future. The content is what matters.
Also, how did you manage to save three files with the same name and extension (wallet.dat) without one of them overwriting above the previous one? If you are on Windows, can you right click each of those files and go to "Properties" to see in which extension is the file? Because it could be something like "wallet.dat.txt", where the .txt part is hidden by default, so you only see the "wallet.dat" part. Just curious about that.
The Major Question: Did I misunderstand the tutorials and forums? Are you able to Create the "FILE NAME" and name it whatever you want as long as the FILE TYPE Remains a Wallet Data ( * .dat ) File ?
Exactly.
Is it possible for me to just RENAME the files and still be able to recover my wallets via my backup methods?
Yes. The name doesn't matter.
Can I just Back Them Up Again, keeping the File Type the Same but changing their name from "Wallet" to:
1. My Bitcoin Wallet
2. My Ether Wallet
3. My Verge Wallet
That't what I would do.
I'm currently using only one Flash Drive to back up all 3 Wallets, is this OK to do? or should I have a separate Flash Drive for each specific wallet?
Yes. But having multiple Flash Drives (for all 3 wallets, and not one per flash drive) would be better. What if your Flash Drive stops working?