what's going to get to 6inch?

Oscars can get way bigger than that.

So will plecos (I've got a couple in my pond that are more like 12-15inch!)

Convicts... if they get to 6inch, I gotta have a picture of that! I've never seen them any bigger than 4inch.

No special procedure to introduce your pleco.... add a piece of driftwood to the tank (with little nooks and caves) and the pleco should be fine.