I am working on a new site but I want to retain all the customer, sales and product information from the old site. What are all the tables related to these, so I can move them from the old MySQL to the new MySQL db.
Or is it better to move the new CMS, Config and extension tables to the old MySQL install ?
For your requirement, best way is to migrate data from old site to new site. For migration, you need to use default magento functionality of import and export. Export data from old site and import to the new one.