I have some general questions about  that ideally would come form first or second hand information, and not Wikipedia or the web.

How critical was the operation  in terms of running interference for Operation Overlord ?

Does anyone have any first hand accounts of what they men were doing on that beach with the props and inflatables, etc?  Who was there?  A mixture of civilians from Hollywood and armed forces, or all soldiers, some recruited out of LA, etc?  Who was there, and what was it like?

Most importantly, where did that army / group GO after D-Day?  What was thier path, and what else did they accomplish along the way?

Thank you in advance.

It kept the 15th Army at Pas de Calais and north for almost two months, which made the build up and break out possible.

FUSAG was fake, there was no "army" to send anywhere.  It was just radio operators, guys who maintained the fake tanks and planes, and Patton strutting around, making sure everyone saw him.

So those guys just went home after D-Day?

FUSAG contained a number of actual units as well as ghosts.  Specifically, units not intended to land immediately.  The dummy units typically had only a handful of Soldiers assigned, and some of the units kept up the facade long after DDay, for example pretending to be preparing invasions of Norway and Denmark, which as a result kept relatively large garrisons till the end of the war.