Your 3 destinations seem reasonable for 11 days/12 nights. Although I prefer to stay in Paris upon arrival after a long flight, it makes sense to plan your 5 Paris days in the middle of the trip since your other destinations via train involve transiting through Paris.
I have an older RS France guidebook that indicates there are several trains per day that connect CDG to Reims, but it's unclear if this is a direct train (I didn't see this option when I did a quick search, i.e., you'd still have to change trains at some point). That will be a tiring arrival day heading to Reims, but it seems doable.
When you say you'll have 3 days in Beaune does that mean you'll have 3 nights or 4? If only 3 nights, this gives you only 2 full days. I've not been to Burgundy (yet), but I would add another day there, especially since this will be your final destination before flying home. I find travel days/transitions to be tiring, and would guess that this is also true for those with mobility issues. More time in one place allows a slower place, but I recognize it's not always possible to add more days to a trip.
As you note, Burgundy is your farthest destination, and that is a longer train ride with multiple connections to get to CDG (compared to a train to or from Reims). Maybe you're already planning to do this, but I would recommend taking the train the day before your flight home. I've become a fan of staying at an airport hotel the night before flying home, especially from CDG, and especially if it's an early departure. I'm totally sold on staying at the Sheraton in (not just near) Terminal 2 at CDG. We'll be doing that next April...
