The VEA takes about 40-45 minutes to get to the Santa Fe from CDG, but thats only once you have actually left the airport - we arrive at terminal 1 CDG, and thats usually the VEA's first pick-up, so we usually have at least 15 minutes on the VEA while it picks up at the other 2 terminals, before leaving the airport.
So figure around one hour to get from the airport, and one hour back again.
I also think getting the 4pm VEA for a 6pm flight departure is too late. You'd really need to get a 3pm one or thereabouts.
We usually get the TGV train back from DLRP to CDG - that journey only takes 10 minutes, so does give us a good hour extra at the parks before we have to start the journey home.
But, if you already have your return VEA tickets, I do think you need to get a 3pmish VEA for your flight.