OP: Where are you staying? You didn't mention your resort, I don't think (I skimmed some of the replies) and I think that factors into your itinerary.
To me, it seems like there's a lot of coming and going, which can be exhausting, especially after walking 8 or 10 miles a day in the parks, not to mention a lot of standing in line.
If you and your group are all staying onsite, then at least people can come and go as they please. Or does everyone just want you to do all the planning and they'll just follow along?
I never plan for 3 meals a day--that's a lot of time either not going on rides, seeing shows, etc., and/or not relaxing and doing nothing, which is a necessity at WDW. I think 2 planned meals (maybe even that's too many) + snacks is the way to go. But that's just my opinion. You and your group may feel differently about this.
To answer your question--is this overwhelming for first-timers?--I think it depends on who they are, what their stamina's like, and whether or not they're going to like WDW. I mean, of course they'll love it, but maybe they won't?
And that's really pushing it to have a park on getaway day unless your plane departs in the evening. Or perhaps you're driving. DAK is my favorite park, so I'm prejudiced here. I would never save that until the last day.
Is there no way to make your trip even one day longer? A rest day there? RDing 4 days in a row is, even for a RD person like myself, a bit much.
Also, I see you're not park hopping. I'd want hoppers for this short trip, because if I've never been to WDW before, I'd want the opportunity to revisit a park I felt I didn't get enough of. But, of course, that's $$.
Just some thoughts.