You wouldn't get a super active fish with the assessor though IMO, they seem to really like a spot with overhead cover and turbulent flow(like right under a tunze or sure flow ph). Mine will venture out pretty regularly but nowhere near as much as my grammas...
Have you thought about them at all if you really want movement and a docile nature above all else?
You could easily get a very small and a med. size gramma loreto and let them do their thing...I only say 2 because 2 of them will be significantly more active in the water column than 1.
JL often gets nice shipments of them in and no joke after a year and a half of them my harem of 4 still crack me up here and there.
With 2 of them sized as stated you'd more than likely wind up with a male/female pair and would encounter 0 aggression unless they're spawning but with you're docile selection of tankmates I don't think you would have any issue even then.
They WILL fight with their reflection though, but fighting for this fish is just a who can open their mouth bigger competition.
Try that with your reflection sometime...lol