TfW Rail Twitter are sending out Route Factsheets with the improvement plans on them.
Apologies if these aren't appearing properly im working on it!
Ive got hold of the one for Shrewsbury to Birmingham.
They also have a seating/total capacity graphic for the current and future type of rolling stock.
The peak times / services are not defined though its clear that they cover 2 services each way. A c 1000 total capacity in the current AM peak corresponds with 5 Class 158's arriving (the 0829 into New St is booked 6 car normally). (5 x 199 = 995 total) (5 x 140 =700 seats)
The lower capacity in the current evening peak is equivalent to 4 Class 158's departing. (4 x 199 = 796 Total) (4 x 140seats = 560 seats)
An extra 158 will be available for evening peak from December 2019 bringing AM and PM the same.
Then note whilst "total capacity" goes up in Dec 22 once the Civitys arrive seating capacity actually goes down especially in AM peak (by c100!)
Civitys would appear to be 5 x 2 car in AM peak. c 600 seats on graph is equal to 5 x 120 seats and just over 1000 total capacity is equal to 2 x 202 = 1010.
PM peak has 4 x 2 car and 1 x 3 car operating. (4 x 120 seats plus 196 seats is 676 seats) & (4 x 202 total plus 316 total is 1124 total).