To specify discrete inputting go to Devices> TV> Settings> Adjust Inputs> Choose Method 2.
It shouldn't need to learn any commands for the Samsung; they'll all be in the database, maybe with slightly different names.
You don't need to switch each device off separately. Each Activity switches on the devices it needs, and when you change to another activity it switches off those it won't need in the new activity, leaves the others on, and switches on any more that it will need for the new activity.
You use the Off button only when you've finished with all activities for the session, or for the day.