The final layout at Shenfield is a bit different to that shown. The main to electric and electric to main crossovers at the London end are simplified for example.
The key changes are to separate the Crossrail operation from the rest of the GE as much as possible, which can't be done with the current layout. Down Southend trains will benefit from a new 50 mph crossover from the down main into platform 4, and then continue via the diveunder. Crossrail trains will use 5 and 6 as much as possible. Occasional use may be needed of platform 4 for Crossrail depending on the final timetable.
Mathematically 12 trains per hour can be turned with two platforms, assuming 3 minutes for platform re-occupation that gives a 7 minute turnround.
Note the freight loop between Chadwell Heath and Goodmayes is not now happening.