This is the most important point when making microservices. There's lots of talk about bounded contexts but very little about how to draw the boundaries. Most are superficial and repeat bad examples like OrderService (order is both a verb and boun, OrderingService sounds ok). Using two part service names (ContentComposition, MessageDelivery) usually works out well.

As to the shared db aspect, while spitting a miniservice into micro ones I had this situation. All the code was split first and the db changes being the most difficult to was done last as a point.of we don't expect to revert this.choice. We weren't at a performance limit so that was fine, any schema changes had to be clearly communicated and coordinated. In all not too bad. I don't think I'd want to leave it in that state as a normal state. The point of micro is Independence and isolation of changes and sharing a db leaves a sensitive area. Don't let that stop you if it's only a temporary state. Just get commitment as to how temporary that is, since in absolute terms everything's temporary.