How many channels of MIDI/CV do I really need?

So I've been looking MIDI/CV interfaces and there are plenty of them in eurorack format.

However, I've noticed that some MIDI keyboards also come with USB/MIDI to CV interfaces, so rather than buying just a converter I could buy a keyboard that also has the converter.

Actually keyboards such as Arturia Keystep are more affordable than many eurorack USB/MIDI to CV interfaces.

But the Arturia Keystep for example seems to have only one CV out and one Gate Out.
So this is just one channel of CV, right?

But how many does one need?

As many as there are controllable parameters?

Actually, if one purchases this:

http://www.synthtopia.com/content/2016/10/20/the-cv-ocd-is-a-super-flexible-midi-to-cv-box/

Then it doesn't really matter, since that device has plenty of CV outs and costs only $95 plus shipping.

EDITED May 28th 2017, 13:27