…until you need to market to people who didn't get a shipping last month, delay shipping until at least one recharge attempt, or ship before charging for customers you're reasonably sure will pay anyway.

Business changes, and putting rigid firewalls in place without seeing an established pattern of change and without established need for that is a bad idea.

One global database buys you a lot (easy data access, easy transaction consistency, simple locks, even transactional notifications), and you can take it very far performance wise, throwing that away just in case you might need more performance later seems unwise.