I agree with
@LAKid53's recommendations. If you are flying in on Thursday, I probably wouldn't bother with a park ticket for that day either because you wouldn't get much use before you'd need to wind down to rest before the 5K. I live about 6 hours away and tend to hit the road about 1AM Thursday to rope drop one of the parks for a few hours before hitting the expo which gets me some low-crowd park time, but also helps adjust my sleep schedule so that I can actually fall asleep at 7-8PM the night before the first race.
The expo is a madhouse the first day, it will take awhile to get through no matter what time you are there, but if you are flying in, I imagine it wouldn't leave enough time to do the expo and have any meaningful time left in a park afterward (at least not enough to justify purchasing a full day ticket). There is a room with up to several hundred people in a line to get to the line into the merchandise area where hundreds more people are shopping and waiting to check out. Fortunately, the check out is pretty efficient and doesn't take as long as it might look. However, heed LAKid53's advice and at least pre-purchase something (even if it's just a pin or something) because, if you have a pre-purchase, you can skip the big line and enter the merchandise area through a much, much shorter pre-purchase line. Once you are in, you pick up your item, but are still in the merchandise area and can feel free to shop for any other items that strike your fancy (there's a ton to choose from).
During race weeks, I try to eat sensible, easy-on-the-stomach meals (sub sandwiches, steak and veggies, creamy pastas, etc) and don't drink any alcohol until after my last race. Race mornings, I'll get up around 2:00AM and shower, eat some fruit, trail mix, etc. and try to head to the starting line early enough to get some character photos, wander around, stretch, and get to the corrals early enough not to be at the back.
After the races, I'll usually go to my car and towel off and discretely change into something dryer and hit the parks until around 3:00PM and then pick up dinner on the way to the hotel and soak for a bit in a hot bath with Epsom salts for a bit before bed. After shorter races, like the 5K or sometimes 10K, I may try to rope drop Hollywood Studios to get a RotR boarding group or rope drop another park if I finish in time. After a 10K or Half Marathon (if doing Dopey), I tend to choose Epcot (because you're already there) and spend 2-3 hours in the park then hop to Typhoon Lagoon or Blizzard Beach after lunch and soak in the wave pool and lazy river to rejuvenate the legs for 2-3 hours. My suggestion is map out what you think works for you closer to your trip but allow yourself the flexibility to change your plans midstream depending on how you feel that day.
No matter what you do, if you've got multiple races in a weekend (and days in the parks afterward), I highly recommend getting: 1) Body Glide (nothings worse than chafing with a race and three more days of park hopping ahead of you), 2) Nip-eaze (same reason), 3) Bio-freeze (the runDisney aid station will have a ton of it, but I like having my own if I want it for after the race or the next day), and 4) oofos or other heavily shock-absorbent recovery sandal to wear post race with or without socks (allows your feet to breathe outside of shoes to avoid blistering and are very well padded). Also recommended for comfort/utility, 1) a race belt to hold your phone, key, and/or any snack or other item you want with you during the race, 2) Bluetooth headphones (like AfterShokz) to listen to music while running, and 3) a cooling towel (if it's going to be a hot raceday) that you can dump in an extra cup of water and put around your neck after you pass hydration stations.
After the final race, I enjoy a beer or two (if you know you want two, go ahead and get your refill ticket when you buy your first one and avoid a second trip through the line). Go shower and hit the parks until close (or whenever I get to tired to keep going). I usually stay for a full day Monday (sometimes golf 9 holes Monday morning and hit the parks after, or sometimes just do a full day of parks) and usually will do a half day Tuesday and hit the road around noon or 1:00PM.
You can buy it at Publix now, both the gel in a tube and my new favorite, the roll on. I found a new brand of recovery slides - Superfeet. The strap across the top of your foot is a little softer than the ones on Oofos slides. 
