Again, do I need to install Bitcoin Core, or is the portable version sufficient?
Again ? That's the first time you are asking this question.
There is no portable version of core. Running core as a portable version means manually settings the data directory to the portable device.
So.. yes you need core installed. You can't use core otherwise.
The important part is this:
Core needs to be running and fully synced for armory to function properly.
It doesn't matter HOW you have installed it. But it has to be
installed (= running and synced).