Employees: limiting products and adding field

[taloweb]

I would like to customize "Employee" section in the prestashop admin area:

first of all I would like to limit Employees to edit thei own products without the capability to "touch" other Employees products, then I need to add an extra field to Employes properties with a custom expiration date (that they can't modify) and if the expiration date is in the past the Employee can't login.

 

Some hint? I don't know where I can start rof these tasks...

 

thanks in advance