What database architecture to use for SaaS?

Question

Database design

Greetings, I have
an idea to implement a b2b saas project. There were some questions connected with a DB.
Some facts about the project:
1) Companies register, create employee accounts (something like a mini-cmr)
2) Companies can add some site modules, expanding the functionality.
3) Companies have a database with employees, a database with clients, a statistics database, and a couple of other information .. Companies are approximately up to 1000 pcs.
I can’t understand how the database architecture should be deployed and what are the pros and cons of each solution. Should there be one database for the entire system and a separate stack of tables for each company, or should all companies mix data in common tables.
Please tell me +/- , or maybe you know how it is usually implemented.