There is a check box to set the preference for the auto creation of account numbers. Use this if you want system generated account numbers - if maintaining a link with legacy data it may be wise to enter historic, manual, account codes.
Categories can be associated with a either Companies or People, or both. The following have some impact on how the system works
Employee - if a person within the system company is marked as an employee then they will be available in the HR system
Customer - an account marked as a customer will be available in the Sales Ledger (AR) system
Supplier - an account marked as a supplier will be available in the Purchase Ledger (AP) system
If you use the ‘starter’ instance then Contact categories already has ‘Employee’, ‘Customer’ and ‘Supplier’ set up.
Apart from the above there is little setup required in the contacts module beyond the optional classifications you require. The different sections you can use are: