just a couple of points.
you might want to move the right hand rock over a bit, cause where it is presently might make cleaning the glass down that side awkward depending on what your gonna use to clean it.
the last pic you put up looks like a colony of zoanthids so thats a good start, hopefully they'll survive your cycling process!
i'd go for the 1200, its good to have the extra flow as it'll help keep your rock and sand clear from detritus.
also if its a good strong flow you can deflect it with rocks to get good flow through your rock work.