Is 1 filter enough?
-- theundeadwarrior

A stereo filter or two separate filters would be better as you have two possible sound sources without filters (Plaits and Disting Mk4), but 84 hp is small so I'd suggest to keep it like this to begin with.

Still trying to figure out where to get a kick from (I have a disting Mk4 in my other rack that I might use for samples here)?
-- theundeadwarrior

Maybe take a look at Erica Synths Pico Drums, it's small but you can load your own samples on it with a separate programmer chip. I wouldn't recommend to go for a module that does only one sound, like the befaco kickall or one of the tiptop drum modules, because of the relative small size of this system.

Is Pam + mini grid too much for sequencing such a small rack? My idea was to combine gate triggers from both with an OR module to create interesting drum patterns.
-- theundeadwarrior

I think grids work best as a full-size module, the small knobs on the one you have will make it less fun to play with (at least in my opinion).
Grids is a great module but I think in such a small rack you'd have more fun with a more versatile module such as the micro Ornament & Crime. You can easily load the alternative firmware on it, giving you two separate "apps" on each side on the module. This could replace your logic module as well and there are alternative versions that have two of the three grids channels (https://github.com/benirose/O_C-BenisphereSuite).

Overall opinion on this rack: 84HP is quite small to have both you drum, multiple sound sources and keep it playable as well. You mention you already have a few modules, which have quite some HP altogether. These modules can almost be a rack on their own (although mini grids is a bit of an odd one in this but you can use it with melodic stuff as well, to trigger the Percall for example).
If you want to add drums you are going to compensate those modules in size, functionality and playability. Like I mentioned earlier, you can add something like a Pico Drums to the rack, but keep in mind that this won't have as much experimentation opportunities as the other modules you have.

If you are willing to keep some modules that you already have gathered out of this rack (for now), you could add some more drum-related modules into it, but of course the tradeoff would be less modulation for the melody part.
Another option would be to have a small drum synth/groovebox outside of you rack and use a CV/Gate to MIDI module to sequence it.