Generally, I would agree with the person above on a Keystep or Beatstep Pro for doing 2-3 voices plus drums/event triggering/etc.
If you like the Ground Control, it does have the advantage of being a standalone unit with its own power supply amd case, as well as the power supply for at least a single rack of modules for if you get another case (up to 1A of +12 and 700 mA of -12, though you'd want to avoid going over about 70-80% of that to avoid harm from voltage spikes or modules that need more power to load up and start) and take it out to be racked. It is very expensive, so definitely look around to see what else is out there and if it is worth it. There are also more elaborate programming-based options like the Hermod (the original is very cheap used nowadays) and the Hermod+, or my beloved Nerdseq, but you're not quite there yet based on what you have here.