FWIW, I've got clients using multiple machines (running massive orchestral templates making use of VE Pro "Slave" machines).
These folks are generally hard-core professional composers... scoring for TV/Film/Video Games.
IMO, Your quickest work-flow is generally the simplest.
If your needs are extensive, I'd start with the fastest (single) machine you can get.
If that's nowhere near enough speed/processing to run your projects, then it's time to implement VE Pro Slaves.
Folks that are using VE Pro Slaves, to keep work-flow as streamlined as possible... the Slave machine/s are always running the same libraries.