With the help from a colleague please refer to the answers below:
Regional mboxes can be created using getOffer/applyOffer individually as well as in batch using getOffers/applyOffers. Additionally you can use the FEC using the Target Global Mbox as well if preferred.
Both global and regional mboxes can be used in SPA. Both types of mboxes can be made compatible with a SPA with the right design and architecture.