How to install macOS on a encrypted, journaled filesystem?
I know you have a working answer already, but I thought to share my experience anyway, only updated for High Sierra and using Apple's new file system APFS.

My motivation: I was driven by the (constantly varying) 6-14 hour estimate for FileVault to finish on a new install with no additional user data.

So this is what I did to install macOS on an already-encrypted filesystem - much like yours:


Create a bootable macOS installer
Erase and format as APFS (Encrypted)
Install High Sierra


Pros:


&lt; 10 mins to encrypt by Disk Utility? (possibly less, I didn't monitor closely)
FileVault already enabled.


One main difference is that you supply a password earlier when formatting with Disk Utility, rather than being given one (the Recovery Key) when enabling FileVault post-install.

Hope this helps someone.