My suggestion is that we meet up in the afternoon for lunch or snacks at the McDonald's. We meet up first at Shell Ultra South on N1 in Midrand at 1pm, drive to McD's off grayston offramp, have lunch or snacks there, and if possible leave our cars there and walk to the public viewing area to check out the F1 cars. It is possible that we may not be able to leave our cars at McD's, in which case we try and park in Sandton City or somewhere else. At least once we are there we can decide how to proceed. If McD's is too full, we could try KFC next door, or else we go to Village Walk or McD's in Rivonia. The F1 cars are on from 3pm to 4pm, according to the programme.
According to the site, these are the parking areas (which are quite far):
Sandown High School
Corner of Rivonia Road and Corlett Drive
Innesfree Park
Cathrine Extension
(below Grayston Drive Bridge)
Wanderers Club
21 North Road
Illovo
Inanda Club
1 Forrest Road
Inanda
Sandton