Configuring a validation rule to require a field for a specific record type is the best way to ensure that important fields are entered and formatted correctly. Updating the important fields to be required on the page layout will not prevent users from entering invalid data using other methods, such as data loader or quick actions. Making a formula field to check the format of the important fields will not prevent users from entering invalid data, but only display a message or an indicator. Creating a workflow rule to check the fields are formatted correctly will not prevent users from entering invalid data, but only trigger an action after the data is saved.