I haven't done the breakfast or pasta in the park (I'm usually on the dining plan, so that seems like excess money when I'm already paying for my meals), but I have done the after party at DTD. That's more low-key, you don't need to purchase a ticket to attend. Wear your finisher medal and you'll get discounts at the shops. You'll see LOTS of us there winding down from race day. I usually schedule an ADR for dinner at Raglan Road for us to go and enjoy the Irish music & dancing.
When it comes to planning your days out, it looks like your trip plan is the exact opposite of mine. As in, we plan our major park days for after raceday. We don't want to tire our legs out before we've even laced up our running shoes, lol. We plan to arrive early on Thursday the 18th (around 10am), then head to the Expo while we wait for our room to be available (it wasn't this year, until around noon). By the time we get back from the Expo with all our race gear (shirts, bibs, pins) and souvenirs (I get a new Sweatyband or two every year, and sometimes a tank or t-shirt), we're ready for a late lunch and a nap. ADR for dinner, then relax and go to bed early since the 5K is in the morning.
Friday: 5K in the morning, return to the room to shower & possibly catch a quick catnap before lunch and then heading to Animal Kingdom for the afternoon. ADR for dinner, early to bed since the 10K is in the morning.
Saturday: 10K in the morning, return to the room to shower & possibly catch a quick catnap before heading to Hollywood Studios. ADR at Sci-Fi, Fantasmic! that evening, QS dinner at either The Mara or Riverside Mill (they have a create your own pasta bar). Early to bed, since the Half is in the morning.
Sunday: PHM day! Return to the room to shower & catnap. QS lunch at The Mara, chill at the resort for the afternoon, ADR for dinner at Raglan Road for the PHM after party & shopping.
Monday: Free day (no parks). Either resort hop or just chill at AKL.
Tuesday: Epcot
Wednesday: MK
Thursday: Check-out & head home. Depending on how late our flight is, we might head back to DTD for last minute shopping & to pick up lunch and/or snacks leftover on our dining plan.