Glad you are the cautious type and did some research, too. Yes,
eraseDisk will remove all volumes and replace it with a single new one.
I believe when you encrypt Time Machine, the whole partition becomes encrypted. That's why there's a coreStorage partition type. You can use the command
diskutil list to show all partitions on attached devices. I'm guessing the partition containing the encrypted Time Machine backup will be coreStorage. (I really should encrypt one of my volumes so I have a first-hand reference.)
You should be able to revert the TM partition to an unencrypted partition by going to the TimeMachine pref pane (in System Preferences), selecting your current TM partition and unchecking the "encrypt..." option. Not having done that myself, I would suggest, if at all possible, making a backup of your TimeMachine backup. Though, OTOH, it does sound like you're willing to start fresh and erase it. That point does remove some risk

.
Hope this helps point you in the right direction, in any event.
Btw, if for some reason the TM pref pane doesn't remove the encryption, take a look at the
diskutil coreStorage revert command - though it has some limitations regarding how the coreStorage encrypted partition was created. For the most part, as you might have guessed, DiskUtility is the GUI front end for
diskutil, and several other tools.