I don't know that you need an entire "rest day", but it does seem like you have a nice mix of busier days and not-so-busy days. Are you counting on the twins sleeping in a stroller? If so, do they do that now? I ask, because not one of my four kids would sleep in a stroller. Ever. I would look at the parents serenely pushing sleeping toddlers with naked envy. Obviously, the fact that mine wouldn't stroller-nap affected our touring style.
The other thing I would stress to you is flexibility. You seem to be willing to switch things up if needed, which is good. I would just keep an eye on the kids, make sure they're still having a good time. If you need to drop an ADR or two, well, there will always be a future trip. When my younger DD was 2-3, we realized on about Day 5 or 6 (slow learners!) that, if she needed a break or to get out of something, she'd just wet her pants. It was quite effective. Just a reminder--kids have a way of letting us know when they've had enough...
I'm not counting on them sleeping in the stroller. The main reason we picked CR was so we could return to the room easily from MK (where we will spend the most days) for naps if needed. If they sleep in the stroller, great, but if not I'm planning to head back. They have not napped in the stroller since they were young infants, but admittedly I haven't really had them out for a full day at an amusement park or similar yet. I'm kind of strict (some would say crazy?) about their nap time right now so we plan around it for the most part.
I'm definitely prepared to be flexible, because it's so hard to plan when I'm not sure how they will be in 6 months. So much changes week to week with them, so it's just too hard to predict.