Permission on a field

Hi I have a question about assigning permissions.

I have field on the purchline that I want to restrict to 'view' except for a particular role.

So, here's the plan...

1.  Go into a role that has permission to the field in question. (such as the Purchasing Agent).

2.  Override the permission on that field to 'view'

3.  Click on 'Apply to All Roles'

4.  Create a new role

5.  Add the Purchline to the Forms part of the Role

6.  Add the field in question.

7.  Set permission on the Field to 'update'

8.  Add the Role to whoever needs to update that field.

...sound good?

Thanks in advance.