It only requires an optical trigger for each flash to fire multiple guns simultaneously. I bought some Metz potato masher type flash for this purpose. I know there is a specially made PC connector with one male port and 4 female port. I'm not sure how that'll work as all flash trigger will be connected in parallel with no isolation between them.
I can think of an easy way to do TWO flash alternating with latching relays but more than one, I am not sure.... We probably don't want to over-complicate it for it will have to work reliably every time - and in less than optimal conditions. I can't think of how timer'ed approach is useful.... is that going to be like an intergovernmental type installation??