the difference between multiply and sum, is exactly like you learned in the school (but applied to voltages) , depending of the case you will prefer use one or other.
considerate this: if you have a first voltage, and you add as sum a second voltage , the result voltage always will be an offset of the first one
multiplying voltages work a bit different for instance if one of the voltages is zero, the result always will be zero until the initial voltage change , also decimal matter , if you multiply a voltage by 0.5, you will get half of the first voltage , and so on
for all the 1 to X in you list, you can connect whatever arbitrary number of cables in a output
for all t the X to 1 in your list you could mix whatever arbitrary number of cables (using mixers , sum, etc ) then, connect to the input
one more thing, there are not difference between the nature of the signals, all them are voltages, you can use a module for all purpose, you can use the unity (for instance ) to mix cv ,audio , triggers or whatever