Yes, you do need to mount, but the “grep luks” part won’t work if you’re going the unencrypted route.
I’d advise you follow the “quick” version (BTRFSonLUKS copy&paste) and change according to this post.
The outcome will be identical to the wiki article you’re referencing.
Adapting that Wiki article would of course also work; just haven’t done that yet.
[Edit] You can always add other partitions and mount via fstab after the install.