To answer your last question first, if access privileges are set so that a given user can't see certain records, when a find is performed, it's my understanding that FileMaker won't find the records to which they don't have access. Show All Records, on the other hand will bring up all records and the user will see the <No Access> screen for those records.
You could use conditional formatting to set the field's fill and text color to match the background to make them disappear. The conditional format expressions would check the user's privilegeset name to determine whether to apply these formats.
You could also create more than one layout for the data. Scripts attached to buttons or even layout based script triggers can check the user's privilege set name and switch the appropriate layout for them.