Me again, I re-read and saw you also asked about watching.
My DH got on a bus with me to Epcot the morning of, monorailed to the Polyneisan and cheered me from there. I'm not very fast so I think he might have been able to catch me at the TTC and then move to the Polynesian as it's not a far walk.
He then went to MGM and waited for me at the start of the path to the S/D and Y/B/Boardwalk area. From there he jumped a bus to Epcot but then had to make his way to the finish area where the family reunion tents are. He was about 20 minutes behind me but he had waited for my friend to pass him at MGM before he got on the bus which I'm sure he had to wait a short bit for
Now my Mom took a later start on our instructions

She left the hotel on a regular bus to the AK park and waited for us around the bend between that store that is outside of the park and the bus drop. After we passed she jumped a bus to Epcot but per my request she went INSIDE Epcot and waited between the Electric Umbrella and the Guest Service building. This was so I could drop off my water bottle before the finish line so I was free of 'stuff'

She too waited for my friend and then met us in the family reunion area.
I'm not sure but I think my DH was lost in the parking lot a bit because he finally showed up after a few calls between me and my mom and then Mom showed up.
This year Disney had a spectator tool they loaded I think it was in December that you plugged in your runners pace or planned finish time and it gave times for you to be there and I think it included approx travel time for the spectator to get there.
It's a great weekend I hope your group enjoys it as much as mine does
Happy planning!!!!