Ah - I didn't realize that you still had the Mother 32. In that case, it should be perfectly fine to use the "KB Output" and "Gate Output" from the Mother (note though, that the Mother outputs -5V to 5V for V/oct, and I believe that the Plaits need positive V, so you may need to go up five octaves on the Mother to get positive V/oct ... or you can use Maths to add offset). But to get started, I really don't think that you need anything else at the moment (if anything, the Disting).
Another good advise is to go slowly in the beginning. It really is impossible to anticipate what you will find interesting and what you will eventually need. So start with a few modules. Push them as far as you can. Then it will become clear where to go next. The journey is the destination. :)