Hey there,
in short and dirty =) You need to try your case practically and see/feel how it functions together as an ensemble.
Sacguy71's suggestion to trial within VCV Rack software I +1.
Marbles goes GREAT with the BIA but as well features the x path for CV modulation linked to the t path triggers...super versatile...look into rebuilds to save on space within your case.
I am not 100% bought in to the 4 channel VCA to perform both mixing and gating duties...maybe Maths could play a role here too...you will see when experimenting in VCV.