I’m pretty sure there is no more complex puzzle than this in modular. 
Generally speaking, you’re probably going to be better served by more rudimentary sequencing building blocks than by complex “black box” sequencers, because the more they do, the more they tilt toward the premeditated and “programmed” rather than the interactive in-the-moment. But that dumps you into an overwhelming number of possibilities. You have to start somewhere, probably by carefully breaking it all down. One way to look at it is the nature of the interactivity that a tool offers.
For example, PP is a manual sequencer without Brains, so it’s basically a manual four position voltage selector, plus the pressure output. Do you clearly see what that does or does not buy you? Adding Brains, the interactivity that is added to the above is mainly the ability to override Brains with your finger. Any interactivity involving your finger on PP leaves timing in your hands. If you want to influence Brains on the clock, you may want some external manual gate source so that you can manipulate Brains’ gate inputs without disturbing PP.
A similar analysis can be done of René, whose interactivity is a bit similar: in addition to manually overriding the pattern (by holding fingers on plates and/or latching), you can “play” the gate and access pages. But only you can determine whether that buys you something you want.
Sometimes the best options lie outside the sequencer, such as using manual input modules (e.g., joysticks or the ADDAC 300 series) to mix input into a patch downstream from the sequencer.
Or as @Starthief points out, if you don’t mind scripting, Teletype offers a unique option to devise your own interactive models.
p.s. Don’t overlook outboard options. Yes, it’s a pain to have one more separate thing, but on the other hand, sequencers gobble HP like crazy, and HP costs $$$. For example, have you looked at the Analogue Solutions Generator?
