There have certainly been shambolic elements to Edinburgh's organisation in past years... I expect they won't repeat the finish line mistake from last year. So, generally speaking, it's not a bad run, as long as you aren't expecting Edinburgh city center. This will be my 3rd emf.
re: the trip back to town... to avoid the bus lineups and trip time, go to the Wallyford Rail Station (it's the upstream/uphill one). Trains are infrequent -- hourly, I think -- so have the schedule/map printed beforehand. Allow at least 15 minutes to get up the hill on tired legs. That train will drop you happily (and quickly!) in the middle of town at Waverley Station.
In the instructions, it's also noted that they've gone to gels and water in place of the traditional lucozade/water. Try the gels beforehand to see how you feel about them and make alternate plans if you don't get on well.
Beyond that, have fun and gently ask the Met Office to deliver good weather.