a) They can offer an option for National and for International. Following our next WC Vendors Pro release, version 1.4.0, they will also have the option to set Max rate per order, free shipping if the order is over “x” amount, and a few other options. Each of these default rates that they set for their store can also be overridden on a per product basis as well. Otherwise, they cannot set a rate for express, standard or free.. or something like that, no.
b) Not from one vendor, no. they’ll have one set rate per product depending on if they are national or international.
c) There will be different shipping rates per vendor. It will be clear that there will be parcels form each vendor- especially after our v1.4.0 update.