Of course you can add peripherals. I much prefer all-in-one package. Set up, plug in and play.
For studio work where you never take the Kb out gigging it's fine to have all the extra devices hooked up you need for your projects, etc, or at home.....
But it really doesn't make any sense to lug all that gear around day after day playing jobs and setting up in different venues each night,.... so the less is more "All in One" KB is preferred IMO.