Also as regards the compositing results, you may find you get the look you’re wanting if you stack multiple copies of PI on the same layer in Premiere, as opposed to creating separate layers for each PI instance. When you stack them on the same layer you can still use the default “classic” compositing style which typically gives the cleanest looking soft edges assuming the underlying clip you’re applying to is opaque. Each copy of PI in that case would composite the new particles immediately onto the previous stage, as opposed to building up separate copies with alpha channels on separate layers which then requires apply modes to be used to help with the compositing of soft edges.
As for Mocha, you would need a separate copy of PI for each effect that requires different masking, so again stacking multiple copies of PI is the way to go. Your decision at that point is whether to stack them on separate layers or stack them all on one layer. Stacking them all on the same layer is probably more likely to give the compositing you’re looking for so that’s the place to start, and if that doesn’t work then exploring the additional compositing and apply modes makes sense.