The Beosystem 5000 is a complex system. I never did like t until I owned one and ended u loving it.
Maybe your problem is related to a common fail of the system that is the ribbon cable between the keyboard and the system. It needs dismantling and work, but if you’re not afraid of fixing the CD50 or the BC5000 it’s nothing beyond usual abilities.
The “Big” Remote is mandatory to program the system, which was a breakthrough feature in it’s time but not so useful nowadays. For everyday use the “little” remote is more useful (volume, source…). Nevertheless, when owning an BS 5000, the MCP5000 is a very impressing thing to have and very usefull too, even if you dn’t need to program any record.
Search in the forum 2012-2022, you’ll get plenty if not all the information you need.