Just to clarify:
You said you wanted to be able to make ambient and also upbeat dance music. Will you be doing this alongside the TR-6S, or do you want to do everything in the rack? I just ask because you mentioned you want the rack to sequence itself.
Knowing this will make it a lot easier for me to make suggestions.
Beyond that, it's time to start looking at modulation and utilities. Three voices, even with two in 2hp format, is a lot to keep track of. Function generators/loopable envelopes are always nice because you can experiment with different kinds of events. Attenuverters and VCAs will also be really important, since it will allow you to control amounts/positions for modulation and give you more control. Maths is a good place to start and see how these kinds of simple but potent circuits can improve your system (this stuff is the heart of modular and makes the more feature-heavy/obviously cool stuff work), but you'll probably need more than that to service all the voices in your system. Hopefully you still have the standalone case for that West Pest - you'll need that space later on.
Also, I would suggest just running through every single function on the Disting. All of them. Just to get a sense of what they are and whether they can help you or if you need them in a standalone module with more control. If there's a mode you don't understand, learn it.