We did a trip to Les Arcs last year and loved!
One tip: since you said you'll be there for about 4 days. Keep in mind you'll probably have not enough time to cover all Paradiski each day(it's huge!). Just the Les Arcs terrain have several pistes/miles. We skied this side of the mountain about 3 days and not repeat many ones. So, search for the lift ticket for the Les Arcs domain at first and Paradisk when you had cover this side. But, of course keep an eye on the promotions!!!
Important, don't forget to get a map with the estimated time you spend to go / back from one side to another. You'll realize that you'll need to keep at least 1 hour to start to get back and be able to come to ( i.e) 1600, before the lifts stop to run. Other way... it's better you have some Euros to get a taxi to back home!
The Narc comment is perfect.
"... TGV service is excellent. I settled on Les Arcs because the funicular runs right from the station, it also means you can pick up food etc. very cheap from the supermarket in Bourg St. Maurice before heading up there. Once you get to 1600 there is a free bus service to 1800, 1950, 2000...."
I would say that's possible to stay at Bourg St. Maurice(cheaper) and get the Funicular to heading up every day to 1600 and start to ski right there. With a good snow coverture you can ski down to Bourg at the end of the day, other way, Funicular!!
BTW, try this other site http://snowheads.com/ski-forum/ there are a lot of information about Les Arcs.