The minimum requirements for what data to transfer is very dependent on how you will use the system.
For basic posting of financial transactions you do not need more than you chart of accounts.
Then you must add customers if you want to do invoicing. And items and unit of measures if you want to do inventory.
For handling purchase you need vendors.
Then there is a whole lot of posting groups that you will need. If you are transferring data from another system than a prior version of Business Central / Dynamics NAV you will most likely have to insert most of these posting groups manually.
But it is really your planned use of the system that decides what data you need.
If you are completely need to Business Central i would recommend this book for you :https://www.hougaard.com/book/
That book will guide you through what you need to get started.
