We both had Fitbits on and we didn't walk as much in the theme parks as I had thought we would, we averaged about 20,000 steps a day but since we couldn't wear them to the water parks, I don't know how much we walked but I would certainly say it was on par with the theme parks and maybe even more tiring due to the countless floors climbed. I'm hoping that there's another option besides stairs once Volcano Bay opens.
I know exactly what you mean about the differences in parks between theming and rides, the order you visit in can completely change the feel of a park depending on your previous few days.
One thing I had wished we had done but always seem to do this way, is do Magic Kingdom later in the holiday and Busch earlier. The reason we always do Magic Kingdom early is because I think it sets the tone for the holiday, once you visit the castle, you know you're at Disney. The reason I wished we visited later is that it's a long day and once the jet lag kicks in, it's a nightmare at night once the night time parades and fireworks start. A few members have suggested staying in the park for an hour after the fireworks finish as it allows the park to empty out, the queues for the monorail/ferry to die down and the rush to be over in the car park plus it's a nice way to relax after a busy day. The reason I've always left Busch to later in the holiday is to get more comfortable driving before driving an hour from Orlando. I felt far more comfortable driving this year than I ever have and it would have been nice to use the early morning jet lag rises to get to Busch early.
I think going to Food and Wine completely changed the feel of EPCOT this year. If you're driving, I'd recommend getting an Uber to the park and having a few drinks around World Showcase.
We did MK first too for those reasons but held off on Universal for 4 or 5 days to spread the top parks around a bit. Tempted to do Busch early this trip but not day 1...I don't like the idea of travelling to the USA to do more travelling to get to a park straight away. We may even skip it this trip and swap it out for Discovery Cove.