Is it possible to remove account module and to work only on sales and buying models
Welcome to ERPNext!
No need to remove a module the beauty is everything is included right out of the box, so all is maintained and supported together as a unit.
However you can selectively hide them https://erpnext.org/docs/user/manual/en/setting-up/settings/module-settings
As well as control user access with this https://erpnext.org/docs/user/manual/en/setting-up/users-and-permissions
edit: Here’s the current modules list (with their associated model DocTypes) https://erpnext.org/docs/current/models