I only plan on adding 1 blue reef chromis fish. And then the 2 clowns that were there first. I will adjust and create 2 more caves just incase. But nobody in the tank is showing aggression, actually all are getting along and sometimes swim by each other with no curious pecking. The only fish that got super curious was one of the banggais to the diamond goby. But that stopped after half a day.Now you mention it, the only really large territory fish are;
DWG, Clowns and the Chromis.
The rest are all lower in territory size.
IMHO the older fish will only kill new inhabitants if they’ve been introduced incorrectly or the tank is too small. I have a 4’ tank and a 18” RS Max Nano. Both of which are over a year old and adding fish to them is more than easy, I even have a Ctenochaetus binotatus in my 4’ tank which is “aggressive” apparently yet it avoids all new fish.