alright. so i found the wallets folder that has folders for both wallets i created. i can open each folder and now locate each "wallet.dat" file for each individual wallet. couple more questions
1) is there any reason i shouldn't just copy the entire "wallets" folder and save it to a few flash drives and burn it to a dvd, instead of ONLY the "wallet.dat" files themselves?
2) for each "wallet.dat" file, i can change the name in front of ".dat" and it won't affect the file, but i would need to change it back to "wallet.dat" when try to restore, correct?
3)
I've never used Bitcoin Core's File > Backup Wallet... feature, but instead always just manually copy my wallet.dat (ideally when Bitcoin Core is not running). , so I see no reason to make an exception for Bitcoin Core.
It is good practice to actually test your backup before relying on it. Testing is as simple as running it in Bitcoin Core.
when you say "I create all my backups on a file system level" do you mean you are backing up your entire linux? or the entire .bitcoin folder?
and when you say "testing is as simple as running it in bitcoin core" are you saying just change out the existing wallet.dat file with the one in just copied?