My DH and I have done the 3rd week in August the last two years. Here are my suggestions:
1.) Get to the park for rope drop or EMH. We would be able to ride most of the rides we wanted to go on, leave around 11 or 12, do some swimming, maybe take a nap, grab some food at the hotel or go for our reservations at the park we are going to at night, head to the other park or the park we went to that morning (preferably one that didn't have EMH. More on that later).
2.) I don't really recommend evening EMH EXCEPT if it's at Epcot. We tried doing both MK and HS over the past two trips. We found that they were still extremely busy up until closing and there wasn't much to get on. Epcot was still busy but you can still check out all of the World Showcase. When we did it, everyone was in Future World so it was nice and quiet at World Showcase.
3.) Definitely take the break in the middle of the day. It's Florida in August and it is HOT. However, it's also my ideal time to go. It's less crowded than the rest of the summer (a lot of Florida schools are getting ready to go back to school or are already back in school), which means shorter wait times. There still will be wait times, especially on the water rides. So make sure you FP+ Kali River Rapids and Splash Mountain. But back onto the break in the middle of the day! After a few hours in that heat, you'll be sweaty, tired, and hot. You will have a fine layer of sweat over your entire body and puddles of sweat in other areas lol. Take the break to cool down and de-crankify.
4.) I recommend getting the park hoppers so you aren't confined to one park a day. If you go to EMH in the morning, chances are everyone will be. However, the guests who didn't get the park hopper will be there all day and night which makes for a very crowded park. DH and I used to only do one park a day and then once we got the park hopper, we'll never go back.
5.) We were picked to test the FP+ this past August. At the time, there wasn't a tiered system for any of the parks but I do have some tips with making your reservations. Make your reservations for the 2nd park you go back to at night. We made the mistake of making the reservations for the morning park so we were out of luck when we got to the park at night. Also, spread them out for where you think you will be throughout the day. We did a lot of back and forth because we wanted to make sure we got everything done.
I hope this helps! Sorry for going off on tangents! Lol