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I can't tell from your posts how much you have experimented with synths or modular in the past, but the general idea of a modular rack is that each module is an individual circuit (or collection of circuits) that suit a very specific function. What's cool about it is that you can re-route those circuits to do interesting things that can't necessarily be done with a hardwired synthesizer or pedal.
So, you probably want to control pitch, speed, volume, number of delay repeats, reverb swells, etc. over time without having to turn a knob every time you want to adjust something. This is where your choice of modules is very important (especially in a small 88hp rack). A huge harmonic oscillator will be almost worthless without many other modules to make it sing. There will be no way to modulate volume without a VCA. There will be no way to modulate pitch/play notes without a sequencer and envelopes/LFOs of some sort.
If you are just hoping to modulate piano samples and vocals through the Morphagene, something like Make Noise Maths, the Expert Sleepers Disting EX, XAOC Batumi, or something of that sort may come in handy. Clouds or Arbhar are interesting granular synths that you could use for vocals to maybe get the "cascade" effect you mention. But you will still want VCAs and other utilities to control the levels of your modulation.
Basically, modular allows you to build a completely unique and personalized synth or effects unit one circuit at a time and rewire it as you please to do different things. It will be difficult to build a versatile instrument in 88hp. It can be done, but it will require a considerable amount of research, and perhaps a sizable financial investment. You may receive some good module suggestions from the other folks here.
Have fun and good luck!