Breather bags weigh heaps and add a significant price to shipping costs. If you use breather bags, you fill them up completely with water and remove the air, then seal them up. The gas exchange occurs through the plastic sides of the bag where it is in contact with the water.
Don't send them MTS, they are a pain in the butt to get rid of once they are in the tank.
If you do send MTS, put them in a separate bag so they don't pop the bag and kill the shrimp during transit. Make sure you double or even triple bag them.
Plants, snails and shrimp don't need a lot of water when shipping. I would put the plants, shrimp and Ramshorn snails in a normal fish bag with 1/3 water and 2/3 air. Seal it up and then put it into a second bag that is sealed up. Put it in an esky with some scrunched up paper or a couple of bags filled with air, to stop the main bag from moving about.
Try to ship them overnight. Plants like Anacharis/ Elodia tend to fall apart if left in the dark for too long.