How to verify all the required Salesforce permissions

Switch to Classic View Mode.

Navigate to Manage Users > Profiles, locate the profile you want to edit, and click Edit. This is what the Profile Edit page looks like.

Under the Administrative Permissions section, make sure the Modify All Data check box is selected.

Under the Standard Object Permissions section, make sure the permissions Read/Create/Edit/Delete/View All/Modify All are selected for Accounts/Contacts/Cases/Leads.

Navigate back to Manage Users > Profiles, locate the profile again and click on the Profile Name.This is what the Profile General page looks like.

Under the Field-Level Security section, ensure the permissions Read Access/Edit Access are all selected under Accounts/Contacts/Cases/Leads Views.
Note: Some permissions, Read Access/Edit Access, cannot be selected due to restrictions from Salesforce. This is what Account View looks like.