Are you travelling by the VEA Navettes coach ?
That takes about an hour or you could book a private shuttle, which would probably be a little quicker or I believe if time is of the essence the TGV raillink takes about 10 minutes, we've never done it but if that's the way you want to go then there are a few members who'll be able to help you with info.
Yes you'll be able to leave you bags at the luggage storage area, official time for the rooms is around 3.30pm, but once you hit the parks you're not going to want to leave until they kick you out. 3 days should give you enough time to do everything, what days, dates are you there, weekends are busier than weekdays, school hol dates busier than mid term. I'd suggest a day in the DLRP park, a day in WDS and then the last day to redo your favourites. Are you staying in a Disney hotel ? If you are and Extra Magic Hours are available, make use of them, it makes such a difference, set the alarm for 6.30am (use the wakeup call on the telephone, it doesn't cost anything and it'll be Goofy on the other end, reminding them they've a busy day ahead, it always puts me in a good mood and raring to go

), breakfast at 7.00/7.30am and be at the park gates at 8.00am. Don't worry if you've a later breakfast slot they won't trun you away earlier and the early slots are far more pleasant as the restaurants are less busy.
Make use of the FastPasses and always get an FP for every ticket, so if the braver ones want to go on SM, twice in a row, then they can use the younger ones FP's to do it. Any more questions just ask.
