Never mind
After actually looking up what happens when you add a new drive (Unraid takes the array offline, clears the disk with 0s, takes the array online again, so that no parity changes) it makes more sense to add the additional parity drive while pre-clearing the 2 data drives I plan to add at the same time.
Gonna mark this one as solved and not deleting in in hopes that may help someone else in the future.