Hello and welcome to the forums,
Yes, what you're asking for is possible to achieve in EPESI 1.3 using the permissions editor alone. To access permission editor, log in as superadmin, go to Menu->Administration and then "Record Browser". You can select the recordset at the top and edit access in "Permissions" tab.
The best way to achieve that is to add new value in Contacts/Access labeled, for instance, "Salesman". Then, add this access level to all regular employees and change the permissions to sales, contacts, companies, etc. to use "Access: Salesman" clearance instead of "Employee".
Then, create the user for your engineer, create contact for him and make sure the contact is an employee. Finally, Add permission in Tasks, so that any employee can view records assigned to him/herself.
The permission editor is still waiting for a proper manual, but most of the minor changes should be fairly easy to apply. Please tell us if and what kind of difficulties you may have using the permissions editor.
Kind regards,
Arek