Using the assumptions that:
- There will be 32 trainsets,
- the trainsets will have a total of exactly 9,120 passenger seats,
- the information about the trainsets I posted above, and
- there must be a whole number of each length of trainset (no fractions or negatives).
Using some math and bruit force, I have a guess that there will be the following number of each length of trainset:
Extra short 7
Short 7
Long 10
Extra long 8
From this, I determined that there will be the following number of each type of car:
Business 3A 32
Business 3B 18
Economy 1A 40
Economy 1B 33
Econ.Cab 4A 32
The biggest assumption is that the number of seats is correct and they didn't round if off. If so, my numbers will be totally wrong.
EDIT: It was pointed out to me that 32 x 285 = 9,120, so it is quite probable that VIA is buying 32 base (i.e. Long) trainsets (thus 32 of each car type) and will reconfigure them as needed.