You would probably want to use an Enumeration for that. Simply specify which possible statuses the customer can have in an Enumeration and bind an attribute of the type "Enumeration" to the customer. You also need to specify which enumeration you'd like to use, so you'd just the one you just defined.
Enumerations allow you to specify icons to match the different possibilities, so in the datagrid you can choose "Image" instead of "text" (the default) under properties.
You can configure the form access by going to the “Security” option in the project explorer. There you choose “Form access”. This should give you options to allow and restrict access to the forms.
For a detailed step-by-step description of how to configure form access you can check the “How To”: https://world.mendix.com/display/Howto/Form+access+configuration