While SharePoint might not be the perfect solution for storing passwords, it is certainly possible to do this in a custom list (like managing any other info).

• M: break role inheritance on list/site, remove unwanted readers/contributors/owners and give security group containing Developers read permissions

• S: give selected developers (or security group containing these) contributor access

• C: create a custom permission level "Add only" that gives access to add but not edit and assign this to specific users or a security group (this has been asked before)

• W1: Not entirely sure what you mean, but if this means that some list items should have special read permissions, just break role
  inheritance on them and assign special read/edit permissions.

• W2: In SPOL 2013 you have access to lists using REST. You could pass this link to your developers.

While SharePoint might not be the perfect solution for storing passwords, it is certainly possible to do this in a custom list (like managing any other info).

• M: break role inheritance on list/site, remove unwanted readers/contributors/owners and give security group containing Developers read permissions

• S: give selected developers (or security group containing these) contributor access

• C: create a custom permission level "Add only" that gives access to add but not edit and assign this to specific users or a security group (this has been asked before)

• W1: Not entirely sure what you mean, but if this means that some list items should have special read permissions, just break role
  inheritance on them and assign special read/edit permissions.

• W2: In SPOL 2013 you have access to lists using REST. You could pass this link to your developers.