I recommend that you do because if you have one aggressive one, then it will help spread the aggression out over more individuals. If it was me, I would quarantine the new angel for 4 weeks, then swap the aggressive juvenile and the new one so that the aggressive one is out of the main tank while the new one settles in, then introduce the aggressive one back after a week or so.
For quarantine to be effective, it needs to last for at least 4 weeks. I usually recommend that 4-6 weeks as optimum and some people will quarantine for up to 24 weeks to be absolutely sure.
Sounds like a plan. Once the new external arrives I can free-up my internal to create a quarantine tank again.
I thought 2 weeks was a pretty standard quarantine time, I do hope whatever caused the death does not become a problem for the rest of the inhabitants.