Aren't the people on here great? Where else would someone so happily volunteer to help a stranger like this? I like to think it's the Disney magic which makes everyone so nice!
First of all, staying onsite is so easy and should not be intimidating to you. You don't have to drive anywhere. Disney will take care of you! We moved our car once in 10 days to go to the drugstore for my eye infection.
I think I'm much better off to go with a plan rather than just going with the flow. I would run all over the place without a plan. If a park looked crowded, I'd just take off and go somewhere else and then end up getting to a park that was actually much more crowded. I don't want to waste all my time running around.
To plan your days, write down when & where each of your ADRs are. If there's an obvious place you need to be on a certain day, mark that on your calendar. For example, if you have a reservation at Chef Mickey's, even though it's not in a park, it's near MK, so you could spend time at MK that day and avoid running around too much. Build on that and make sure you have how ever many days you want in each park.
As a PP said, use easywdw.com to give you the answer on crowds and where you should probably be each day. It's free and he gives good advice. Don't obsess over it, though. If you want your first day to be MK (I would) and the crowd calendar says no, you can absolutely do it anyhow. You just need to use strategies that you used last time to make the day work for you. For example, we got to the parks just after opening and the early mornings were a great time for us to get a lot done. On the other hand, using the example above, if you have Chef Mickey's reservations and he says absolutely not to do MK that day, you could do Epcot and ride the monorail to Chef Mickey's. So, be flexible.
As far as EMH goes, I wouldn't obsess over that either. If you don't have park hoppers, plan some of your days so that you could take advantage of them if you want. If you do have PH, just swing by that park during EMH if you have another park planned for the main part of that day.
To sum up, go with a plan but be flexible. Have a great trip!