Well, if you just use two layers of bending ply, you only have two thin veneers running horizontally where you really need to connect for strength.
I would add a thick face veneer to both sides of one layer.
As for the actual bagging, I would make a form where I bent the whole sheet at full size, then cut the parts from the big cylinderical shaped part.
Rather than having to make a substantial plug to form around inside of the bag, I like to use a big envelope that contains the laminates after the epoxy is rolled on, then bend the whole bag around the form which is outside the bag, and can be made very easily out of cheap ply or sheet goods. Then it only has to be strong enough to support against the springbuck of the sum of parts, which is not much, and only needs hand pressure to hold against the form, while another person clamps some 2x4s long enough to hang off the ends. Once the vacuum is pulled, they aren't even needed, since the pressure on both sides of the bag is so great it will hold the shape even without the form, so long as you don't loose the vacuum.
Bending ply comes in 4x8 and 8x4, with the face veneer running opposite on each option. Shops that edge glue door skins can supply you with single ply faces whatever size you require.
That is what I would do, but I don't' do big volumes.