You will be fine! I just got back and am only around 15 lbs lighter than you, around 5’4” size 28. I also had planned to start a walking regimen beforehand but couldn’t because I ended up with Tibial Tendonitis. We spent 5 nights in Disney before heading to the beach. We had no rest days. Arrival day we did EPCOT from around 1-8, then MK next day from 8 (ppo bog adr) to 6, then AK from 9:30-6, MK again from 8-6, and then HS from 10-3. That last day ended up being shorter than intended because I twisted my ankle and fell the day prior in MK and was really feeling the pain.
All that said, I have horrible feet issues and I made it! You should be fine with your mid day breaks. My suggestions are 1) Take Aleve instead of ibuprofen (if your Dr says it’s ok for you). It did wonders for me! Dr. told me to take 2 every 12 hours so I took in morning and evening. They lowered the directions to 1 when they made it otc but original prescription was 2 twice a day. Definitely check into that! And if the pain is too severe you can take some Tylenol mid dose time too. I had to do that after I sprained my ankle on our 2nd MK day. 2) If you don’t have orthotics, get some! Even if you have a great pair of walking shoes. I use Powerstep. You can get them from Amazon and they even come in wide. 3) Ice! Take some ziploc bags and fill with ice when you go back to your room, prop your feet/legs up and ice for 20 minutes each hour anywhere you have pain and swelling. 4) Frequent short sit down breaks in the park. It does more than you would guess! Even if it’s just a couple minutes. And if there’s a spare chair, don’t hesitate to put your legs up on it. Try to spread out the sit down show attractions like carousel of progress, philharmagic, peoplemover, country bears, etc. so that you have a built in rest time. 5) If there’s a ride that you don’t necessarily want to do but others in your party do (for me it was Astro orbiters at MK) take that time to sit and prop your legs up while you wait. Since AO was so close to Peoplemover, I hopped on that and propped my legs up on the seat across from me and did 2 laps around (there’s never a wait so they will let you stay on) while DH and DS rode AO. It would also be good with waiting on others to ride the Speedway cars since it’s close. 6) Remember to use the train in MK to get around! We had just ridden Space Mountain and needed to head to Splash, which would have been a long walk! So we took the shorter walk over to the train station in Fantasyland and rode it to the Frontierland stop which lets out right next to SM. There were hardly any people waiting and a train pulled up not long after we arrived. 7) Don’t be afraid to modify your plans if needed! We did this a few times. DS 10 loved when I would say we’re going to wing it for awhile.
Good luck! You’ll be fine! Remember to drink lots of water! Ask for free ice water at the QS places. We took Brita filtered bottles and dumped a couple cups at a time in them. Report back with how you do!